diff --git a/exercises/B-hello-world/README.md b/exercises/B-hello-world/README.md
index 27282c4af..ba17f3371 100644
--- a/exercises/B-hello-world/README.md
+++ b/exercises/B-hello-world/README.md
@@ -15,4 +15,6 @@ Inside of `exercise.js` there's a line of code that will print "Hello world!".
 - Try to `console.log()` something different. For example, 'Hello World. I just started learning JavaScript!'.
 - Try to console.log() several things at once.
 - What happens when you get rid of the quote marks?
+  It shows this error : SyntaxError: missing ) after argument list
 - What happens when you console.log() just a number without quotes?
+  When I changed it to : console.log(1234); , it works normally and runs withnout errors.
diff --git a/exercises/B-hello-world/exercise.js b/exercises/B-hello-world/exercise.js
index b179ee953..2ef7f760e 100644
--- a/exercises/B-hello-world/exercise.js
+++ b/exercises/B-hello-world/exercise.js
@@ -1 +1 @@
-console.log("Hello world");
+console.log(1234);
diff --git a/exercises/C-variables/exercise.js b/exercises/C-variables/exercise.js
index a6bbb9786..233a97fe8 100644
--- a/exercises/C-variables/exercise.js
+++ b/exercises/C-variables/exercise.js
@@ -1,3 +1,6 @@
 // Start by creating a variable `greeting`
 
+let greeting = "Hello World";
+console.log(greeting);
+console.log(greeting);
 console.log(greeting);
diff --git a/exercises/D-strings/exercise.js b/exercises/D-strings/exercise.js
index 2cffa6a81..aba14c990 100644
--- a/exercises/D-strings/exercise.js
+++ b/exercises/D-strings/exercise.js
@@ -1,3 +1,6 @@
 // Start by creating a variable `message`
 
+let message = "This is a string";
+let messageType = typeof message;
 console.log(message);
+console.log(messageType);
diff --git a/exercises/E-strings-concatenation/exercise.js b/exercises/E-strings-concatenation/exercise.js
index 2cffa6a81..062b3af93 100644
--- a/exercises/E-strings-concatenation/exercise.js
+++ b/exercises/E-strings-concatenation/exercise.js
@@ -1,3 +1,6 @@
 // Start by creating a variable `message`
 
+let greetingStart = "Hello, My name is ";
+let myName = "Mohammed";
+let message = greetingStart + myName;
 console.log(message);
diff --git a/exercises/F-strings-methods/exercise.js b/exercises/F-strings-methods/exercise.js
index 2cffa6a81..0b5d7e26f 100644
--- a/exercises/F-strings-methods/exercise.js
+++ b/exercises/F-strings-methods/exercise.js
@@ -1,3 +1,10 @@
 // Start by creating a variable `message`
-
+let myName = "Mohammed";
+let myNameLength = myName.length;
+let message =
+  "My name is " +
+  myName +
+  " and my name is " +
+  myNameLength +
+  " characters long";
 console.log(message);
diff --git a/exercises/F-strings-methods/exercise2.js b/exercises/F-strings-methods/exercise2.js
index b4b46943d..e9536f774 100644
--- a/exercises/F-strings-methods/exercise2.js
+++ b/exercises/F-strings-methods/exercise2.js
@@ -1,3 +1,6 @@
 const name = " Daniel  ";
-
+var nameTrimmed = name.trim();
+var nameLength = nameTrimmed.length;
+message =
+  "My Name is " + nameTrimmed + " and my name is " + nameLength + " long";
 console.log(message);
diff --git a/exercises/G-numbers/exercise.js b/exercises/G-numbers/exercise.js
index 49e7bc00b..90dbb4e87 100644
--- a/exercises/G-numbers/exercise.js
+++ b/exercises/G-numbers/exercise.js
@@ -1 +1,13 @@
 // Start by creating a variables `numberOfStudents` and `numberOfMentors`
+
+let numberOfStudents = 36;
+let numberOfMentors = 5;
+let total = numberOfMentors + numberOfStudents;
+
+let message1 = "Number of students: " + numberOfStudents;
+let message2 = "Number of mentors: " + numberOfMentors;
+let message3 = "Total number of students and mentors: " + total;
+
+console.log(message1);
+console.log(message2);
+console.log(message3);
diff --git a/exercises/I-floats/exercise.js b/exercises/I-floats/exercise.js
index a5bbcd852..cf68eb302 100644
--- a/exercises/I-floats/exercise.js
+++ b/exercises/I-floats/exercise.js
@@ -1,2 +1,12 @@
 var numberOfStudents = 15;
 var numberOfMentors = 8;
+const total = numberOfMentors + numberOfStudents;
+
+let studentPct = numberOfStudents / total;
+studentPct = Math.round(studentPct * 100) + "%";
+
+let mentorsPct = numberOfMentors / total;
+mentorsPct = Math.round(mentorsPct * 100) + "%";
+
+console.log("Percentage students: " + studentPct);
+console.log("Percentage mentors: " + mentorsPct);
diff --git a/exercises/J-functions/exercise.js b/exercises/J-functions/exercise.js
index 0ae5850e5..66ea87bea 100644
--- a/exercises/J-functions/exercise.js
+++ b/exercises/J-functions/exercise.js
@@ -1,5 +1,6 @@
 function halve(number) {
-  // complete the function here
+  let temp = number / 2;
+  return temp;
 }
 
 var result = halve(12);
diff --git a/exercises/J-functions/exercise2.js b/exercises/J-functions/exercise2.js
index 82ef5e780..49843f6c1 100644
--- a/exercises/J-functions/exercise2.js
+++ b/exercises/J-functions/exercise2.js
@@ -1,5 +1,6 @@
 function triple(number) {
-  // complete function here
+  let temp = number * 3;
+  return temp;
 }
 
 var result = triple(12);
diff --git a/exercises/K-functions-parameters/exercise.js b/exercises/K-functions-parameters/exercise.js
index 8d5db5e69..dbd50454d 100644
--- a/exercises/K-functions-parameters/exercise.js
+++ b/exercises/K-functions-parameters/exercise.js
@@ -1,6 +1,7 @@
 // Complete the function so that it takes input parameters
-function multiply() {
+function multiply(a, b) {
   // Calculate the result of the function and return it
+  return a * b;
 }
 
 // Assign the result of calling the function the variable `result`
diff --git a/exercises/K-functions-parameters/exercise2.js b/exercises/K-functions-parameters/exercise2.js
index db7a8904b..47dd9d711 100644
--- a/exercises/K-functions-parameters/exercise2.js
+++ b/exercises/K-functions-parameters/exercise2.js
@@ -1,5 +1,8 @@
 // Declare your function first
 
+function divide(a, b) {
+  return a / b;
+}
 var result = divide(3, 4);
 
 console.log(result);
diff --git a/exercises/K-functions-parameters/exercise3.js b/exercises/K-functions-parameters/exercise3.js
index 537e9f4ec..0f2106b52 100644
--- a/exercises/K-functions-parameters/exercise3.js
+++ b/exercises/K-functions-parameters/exercise3.js
@@ -1,5 +1,8 @@
 // Write your function here
 
-var greeting = createGreeting("Daniel");
+function createGreeting(name) {
+  return "Hello, my name is " + name;
+}
+var greeting = createGreeting("Mohammed");
 
 console.log(greeting);
diff --git a/exercises/K-functions-parameters/exercise4.js b/exercises/K-functions-parameters/exercise4.js
index 7ab44589e..4c8e5825b 100644
--- a/exercises/K-functions-parameters/exercise4.js
+++ b/exercises/K-functions-parameters/exercise4.js
@@ -2,4 +2,9 @@
 
 // Call the function and assign to a variable `sum`
 
+function addNumbers(number1, number2) {
+  return number1 + number2;
+}
+
+sum = addNumbers(13, 124);
 console.log(sum);
diff --git a/exercises/K-functions-parameters/exercise5.js b/exercises/K-functions-parameters/exercise5.js
index 7c5bcd605..a5968c0c2 100644
--- a/exercises/K-functions-parameters/exercise5.js
+++ b/exercises/K-functions-parameters/exercise5.js
@@ -1,5 +1,11 @@
 // Declare your function here
 
-const greeting = createLongGreeting("Daniel", 30);
+function createLongGreeting(name, age) {
+  var greeting = "Hello, my name is ";
+  greeting = greeting + name;
+  greeting = greeting + " and I'm " + age + " years old";
+  return greeting;
+}
+const greeting = createLongGreeting("Mohammed", 38);
 
 console.log(greeting);
diff --git a/exercises/L-functions-nested/exercise.js b/exercises/L-functions-nested/exercise.js
index a5d377442..074f9258a 100644
--- a/exercises/L-functions-nested/exercise.js
+++ b/exercises/L-functions-nested/exercise.js
@@ -3,3 +3,18 @@ var mentor2 = "Irina";
 var mentor3 = "Mimi";
 var mentor4 = "Rob";
 var mentor5 = "Yohannes";
+
+function upperCase(name) {
+  return name.toUpperCase();
+}
+
+function greeting(name) {
+  var nameUpperCase = upperCase(name);
+  return "HELLO " + nameUpperCase;
+}
+
+console.log(greeting(mentor1));
+console.log(greeting(mentor2));
+console.log(greeting(mentor3));
+console.log(greeting(mentor4));
+console.log(greeting(mentor5));
diff --git a/extra/1-currency-conversion.js b/extra/1-currency-conversion.js
index 75b3c6aab..0ad40e4df 100644
--- a/extra/1-currency-conversion.js
+++ b/extra/1-currency-conversion.js
@@ -5,7 +5,9 @@
   Write a function that converts a price to USD (exchange rate is 1.4 $ to £)
 */
 
-function convertToUSD() {}
+function convertToUSD(amount) {
+  return amount * 1.4;
+}
 
 /*
   CURRENCY CONVERSION
@@ -15,7 +17,11 @@ function convertToUSD() {}
   They have also decided that they should add a 1% fee to all foreign transactions, which means you only convert 99% of the £ to BRL.
 */
 
-function convertToBRL() {}
+function convertToBRL(amount) {
+  var result = amount * 0.99 * 5.7;
+  result = result.toFixed(2);
+  return Number(result);
+}
 
 /* ======= TESTS - DO NOT MODIFY ===== 
 There are some Tests in this file that will help you work out if your code is working.
diff --git a/extra/2-piping.js b/extra/2-piping.js
index b4f8c4c1b..71abcf981 100644
--- a/extra/2-piping.js
+++ b/extra/2-piping.js
@@ -16,27 +16,29 @@
   the final result to the variable goodCode
 */
 
-function add() {
-
+function add(number1, number2) {
+  return number1 + number2;
 }
 
-function multiply() {
-
+function multiply(number1, number2) {
+  return number1 * number2;
 }
 
-function format() {
-
+function format(amount) {
+  return "£" + amount;
 }
 
 const startingValue = 2;
 
 // Why can this code be seen as bad practice? Comment your answer.
-let badCode =
 
-/* BETTER PRACTICE */
-
-let goodCode =
+//I think it's bad because it's not readable and not maintanable, and not easy to debug.
+let badCode = format(multiply(add(startingValue, 10), 2));
 
+/* BETTER PRACTICE */
+let result = add(startingValue, 10);
+result = multiply(result, 2);
+let goodCode = format(result);
 /* ======= TESTS - DO NOT MODIFY ===== 
 There are some Tests in this file that will help you work out if your code is working.
 
diff --git a/extra/3-magic-8-ball.js b/extra/3-magic-8-ball.js
index 46f65f928..018b4000c 100644
--- a/extra/3-magic-8-ball.js
+++ b/extra/3-magic-8-ball.js
@@ -46,9 +46,13 @@
 // This should log "The ball has shaken!"
 // and return the answer.
 function shakeBall() {
+  return "It is certain.";
+  console.log("The ball has shaken!");
+
   //Write your code in here
 }
 
+let answer = shakeBall();
 /* 
   This function should say whether the answer it is given is
     - very positive
@@ -59,6 +63,7 @@ function shakeBall() {
   This function should expect to be called with any value which was returned by the shakeBall function.
 */
 function checkAnswer(answer) {
+  return "very positive";
   //Write your code in here
 }
 
@@ -101,7 +106,9 @@ test("magic 8 ball returns different values each time", () => {
     );
   }
 
-  let seenPositivities = new Set(Array.from(seenAnswers.values()).map(checkAnswer));
+  let seenPositivities = new Set(
+    Array.from(seenAnswers.values()).map(checkAnswer)
+  );
   if (seenPositivities.size < 2) {
     throw Error(
       "Expected to random answers with different positivities each time shakeBall was called, but always got the same one"
diff --git a/mandatory/1-syntax-errors.js b/mandatory/1-syntax-errors.js
index a10cc9ac2..388ff43f9 100644
--- a/mandatory/1-syntax-errors.js
+++ b/mandatory/1-syntax-errors.js
@@ -1,16 +1,17 @@
 // There are syntax errors in this code - can you fix it to pass the tests?
 
-function addNumbers(a b c) {
+function addNumbers(a, b, c) {
   return a + b + c;
 }
 
-function introduceMe(name, age)
-  return "Hello, my name is " + name "and I am " age + "years old";
+function introduceMe(name, age) {
+  var message = `Hello, my name is ${name} and I am ${age} years old`;
+  return message;
+}
 
 function getTotal(a, b) {
-  total = a ++ b;
-
-  return "The total is total";
+  var total = a + b;
+  return `The total is ${total}`;
 }
 
 /* 
diff --git a/mandatory/2-logic-error.js b/mandatory/2-logic-error.js
index 9cca7603b..37c4ebc15 100644
--- a/mandatory/2-logic-error.js
+++ b/mandatory/2-logic-error.js
@@ -1,16 +1,15 @@
 // The syntax for this function is valid but it has an error, find it and fix it.
 
 function trimWord(word) {
-  return wordtrim();
+  return word.trim();
 }
 
 function getStringLength(word) {
-  return "word".length();
+  return word.length;
 }
 
 function multiply(a, b, c) {
-  a * b * c;
-  return;
+  return a * b * c;
 }
 
 /* 
diff --git a/mandatory/3-function-output.js b/mandatory/3-function-output.js
index 5a953ba60..f390f90f0 100644
--- a/mandatory/3-function-output.js
+++ b/mandatory/3-function-output.js
@@ -1,14 +1,17 @@
 // Add comments to explain what this function does. You're meant to use Google!
 function getRandomNumber() {
+  // this function return a random floating-point number in the range 0 to less than 1
   return Math.random() * 10;
 }
 
 // Add comments to explain what this function does. You're meant to use Google!
 function combine2Words(word1, word2) {
+  //this concatenate the word in the parameter in this case word2 , with the word1.
   return word1.concat(word2);
 }
 
 function concatenate(firstWord, secondWord, thirdWord) {
+  return firstWord.concat(" " + secondWord + " ").concat(thirdWord);
   // Write the body of this function to concatenate three words together.
   // Look at the test case below to understand what this function is expected to return.
 }
diff --git a/mandatory/4-tax.js b/mandatory/4-tax.js
index ba77c7ae2..bc38682ad 100644
--- a/mandatory/4-tax.js
+++ b/mandatory/4-tax.js
@@ -5,7 +5,9 @@
   Sales tax is 20% of the price of the product.
 */
 
-function calculateSalesTax() {}
+function calculateSalesTax(sales) {
+  return sales + sales * 0.2;
+}
 
 /*
   CURRENCY FORMATTING
@@ -17,7 +19,11 @@ function calculateSalesTax() {}
   Remember that the prices must include the sales tax (hint: you already wrote a function for this!)
 */
 
-function addTaxAndFormatCurrency() {}
+function addTaxAndFormatCurrency(sales) {
+  var salesIncludeTax = calculateSalesTax(sales);
+  var result = "£" + salesIncludeTax.toFixed(2);
+  return result;
+}
 
 /* 
 ===================================================