diff --git a/exercises/B-hello-world/exercise.js b/exercises/B-hello-world/exercise.js
index b179ee953..97d0d4d24 100644
--- a/exercises/B-hello-world/exercise.js
+++ b/exercises/B-hello-world/exercise.js
@@ -1 +1,3 @@
-console.log("Hello world");
+console.log("Hello World. I just started learning JavaScript!");
+console.log("I hope I will master JS someday");
+console.log(2);
diff --git a/exercises/C-variables/exercise.js b/exercises/C-variables/exercise.js
index a6bbb9786..18b4246e0 100644
--- a/exercises/C-variables/exercise.js
+++ b/exercises/C-variables/exercise.js
@@ -1,3 +1,5 @@
 // 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..87024cb64 100644
--- a/exercises/D-strings/exercise.js
+++ b/exercises/D-strings/exercise.js
@@ -1,3 +1,5 @@
 // Start by creating a variable `message`
-
+let message="This is a string"
+let messageType= typeof message;
 console.log(message);
+console.log(messageType);
\ No newline at end of file
diff --git a/exercises/E-strings-concatenation/exercise.js b/exercises/E-strings-concatenation/exercise.js
index 2cffa6a81..4df1dd74e 100644
--- a/exercises/E-strings-concatenation/exercise.js
+++ b/exercises/E-strings-concatenation/exercise.js
@@ -1,3 +1,5 @@
 // Start by creating a variable `message`
-
+let name= "Daniel";
+let greetingMessage= "Hello, my name is "
+let message= greetingMessage + name;
 console.log(message);
diff --git a/exercises/F-strings-methods/exercise.js b/exercises/F-strings-methods/exercise.js
index 2cffa6a81..618ef6e65 100644
--- a/exercises/F-strings-methods/exercise.js
+++ b/exercises/F-strings-methods/exercise.js
@@ -1,3 +1,4 @@
 // Start by creating a variable `message`
-
-console.log(message);
+let name= "Daniel";
+let nameLength= name.length;
+console.log("My name is Daniel and my name is " + nameLength +" characters long");
diff --git a/exercises/F-strings-methods/exercise2.js b/exercises/F-strings-methods/exercise2.js
index b4b46943d..1366eff6d 100644
--- a/exercises/F-strings-methods/exercise2.js
+++ b/exercises/F-strings-methods/exercise2.js
@@ -1,3 +1,4 @@
 const name = " Daniel  ";
-
-console.log(message);
+let nameTrimmed = name.trim();
+let nameLength= name.length;
+console.log("My name is "+nameTrimmed+" and my name is " + nameLength +" characters long");
\ No newline at end of file
diff --git a/exercises/G-numbers/exercise.js b/exercises/G-numbers/exercise.js
index 49e7bc00b..8cb50b7de 100644
--- a/exercises/G-numbers/exercise.js
+++ b/exercises/G-numbers/exercise.js
@@ -1 +1,5 @@
 // Start by creating a variables `numberOfStudents` and `numberOfMentors`
+let numberOfStudents=15;
+let numberOfMentors=8;
+let total= numberOfMentors + numberOfStudents;
+console.log("Total numnber of students and mentors: "+ total);
\ No newline at end of file
diff --git a/exercises/I-floats/exercise.js b/exercises/I-floats/exercise.js
index a5bbcd852..bf6c4645b 100644
--- a/exercises/I-floats/exercise.js
+++ b/exercises/I-floats/exercise.js
@@ -1,2 +1,8 @@
 var numberOfStudents = 15;
 var numberOfMentors = 8;
+let total = numberOfMentors + numberOfStudents;
+let poStudents = Math.round((15 / total) * 100);
+let poMentors = Math.round((8 / total) * 100);
+console.log(poStudents);
+console.log(poMentors);
+
diff --git a/exercises/J-functions/exercise.js b/exercises/J-functions/exercise.js
index 0ae5850e5..dee54b401 100644
--- a/exercises/J-functions/exercise.js
+++ b/exercises/J-functions/exercise.js
@@ -1,7 +1,12 @@
 function halve(number) {
   // complete the function here
+  return number/2;
 }
 
 var result = halve(12);
+var result2 = halve(24);
+var result3 = halve(48);
 
 console.log(result);
+console.log(result2);
+console.log(result3);
diff --git a/exercises/J-functions/exercise2.js b/exercises/J-functions/exercise2.js
index 82ef5e780..6d216ffc6 100644
--- a/exercises/J-functions/exercise2.js
+++ b/exercises/J-functions/exercise2.js
@@ -1,5 +1,6 @@
 function triple(number) {
   // complete function here
+  return number*3;
 }
 
 var result = triple(12);
diff --git a/exercises/K-functions-parameters/exercise.js b/exercises/K-functions-parameters/exercise.js
index 8d5db5e69..46e0bb26a 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..01f24cc42 100644
--- a/exercises/K-functions-parameters/exercise2.js
+++ b/exercises/K-functions-parameters/exercise2.js
@@ -1,5 +1,7 @@
 // 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..921bc801e 100644
--- a/exercises/K-functions-parameters/exercise3.js
+++ b/exercises/K-functions-parameters/exercise3.js
@@ -1,5 +1,7 @@
 // Write your function here
-
+function createGreeting (name){
+    return "Hello, my name is " + name;
+}
 var greeting = createGreeting("Daniel");
 
 console.log(greeting);
diff --git a/exercises/K-functions-parameters/exercise4.js b/exercises/K-functions-parameters/exercise4.js
index 7ab44589e..605170757 100644
--- a/exercises/K-functions-parameters/exercise4.js
+++ b/exercises/K-functions-parameters/exercise4.js
@@ -1,5 +1,7 @@
 // Declare your function first
-
+function add (a,b){
+    return a+b;
+}
 // Call the function and assign to a variable `sum`
-
+let sum = add(13,124);
 console.log(sum);
diff --git a/exercises/K-functions-parameters/exercise5.js b/exercises/K-functions-parameters/exercise5.js
index 7c5bcd605..bdcd28f8c 100644
--- a/exercises/K-functions-parameters/exercise5.js
+++ b/exercises/K-functions-parameters/exercise5.js
@@ -1,5 +1,7 @@
 // Declare your function here
-
+function createLongGreeting(name, age){
+    return "Hello, my name is " + name + " and I'm 30 " + age + " years old";
+}
 const greeting = createLongGreeting("Daniel", 30);
 
 console.log(greeting);
diff --git a/exercises/L-functions-nested/exercise.js b/exercises/L-functions-nested/exercise.js
index a5d377442..62f559ffa 100644
--- a/exercises/L-functions-nested/exercise.js
+++ b/exercises/L-functions-nested/exercise.js
@@ -3,3 +3,12 @@ var mentor2 = "Irina";
 var mentor3 = "Mimi";
 var mentor4 = "Rob";
 var mentor5 = "Yohannes";
+
+function capitalLetters (name) {
+    return "HELLO " + name.toUpperCase(); 
+}
+console.log(capitalLetters(mentor1));
+console.log(capitalLetters(mentor2));
+console.log(capitalLetters(mentor3));
+console.log(capitalLetters(mentor4));
+console.log(capitalLetters(mentor5));
\ No newline at end of file
diff --git a/extra/1-currency-conversion.js b/extra/1-currency-conversion.js
index 75b3c6aab..003f7f88e 100644
--- a/extra/1-currency-conversion.js
+++ b/extra/1-currency-conversion.js
@@ -5,7 +5,10 @@
   Write a function that converts a price to USD (exchange rate is 1.4 $ to £)
 */
 
-function convertToUSD() {}
+function convertToUSD(price) {
+  let total = price *1.4;
+  return total;
+}
 
 /*
   CURRENCY CONVERSION
@@ -15,7 +18,11 @@ 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(price) {
+  let priceToBeConverted = 0.99*price;
+  let convertedPrice = priceToBeConverted * 5.7;
+  return parseFloat(convertedPrice.toFixed(2));
+}
 
 /* ======= 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..149b5fad5 100644
--- a/extra/2-piping.js
+++ b/extra/2-piping.js
@@ -16,26 +16,29 @@
   the final result to the variable goodCode
 */
 
-function add() {
-
+function add(a, b) {
+ return a+b;
 }
 
-function multiply() {
-
+function multiply(a, b) {
+return a*b;
 }
 
-function format() {
-
+function format(a) {
+let string = "£" + a;
+return string;
 }
 
 const startingValue = 2;
 
 // Why can this code be seen as bad practice? Comment your answer.
-let badCode =
+let badCode = format(add(10,startingValue)*2);
+// Comment : It is complicated to understand and perfum again
 
 /* BETTER PRACTICE */
-
-let goodCode =
+let sum = add(10, startingValue);
+let totalNumber = sum * 2;
+let goodCode = format(totalNumber);
 
 /* ======= 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/mandatory/1-syntax-errors.js b/mandatory/1-syntax-errors.js
index a10cc9ac2..7124be7bf 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){
+  return "Hello, my name is " + name +" and I am " + age + " years old";
+}
 
 function getTotal(a, b) {
-  total = a ++ b;
+  total = a + b;
 
-  return "The total is total";
+  return "The total is " + total;
 }
 
 /* 
diff --git a/mandatory/2-logic-error.js b/mandatory/2-logic-error.js
index 9cca7603b..88c7a3c7e 100644
--- a/mandatory/2-logic-error.js
+++ b/mandatory/2-logic-error.js
@@ -1,16 +1,16 @@
 // 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;
+  let total = a * b * c;
+  return total;
 }
 
 /* 
diff --git a/mandatory/3-function-output.js b/mandatory/3-function-output.js
index 5a953ba60..e44c32683 100644
--- a/mandatory/3-function-output.js
+++ b/mandatory/3-function-output.js
@@ -2,15 +2,20 @@
 function getRandomNumber() {
   return Math.random() * 10;
 }
+// Comment : math.random gives us a random number between 0 and 1. then we times it by 10, we will have a random number between 0 and 10.
 
 // Add comments to explain what this function does. You're meant to use Google!
 function combine2Words(word1, word2) {
   return word1.concat(word2);
 }
+// Comment : This functions takes 2 parametrs and append word2 to word 1 (combine) and return a new string.
 
 function concatenate(firstWord, secondWord, 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.
+  let wordCombination = firstWord.concat(secondWord);
+  let final = wordCombination.concat(thirdWord);
+  return final;
 }
 
 /* 
@@ -25,13 +30,13 @@ To run the tests for just this one file, type `npm test -- --testPathPattern 3-f
 */
 
 test("concatenate example #1", () => {
-  expect(concatenate("code", "your", "future")).toEqual("code your future");
+  expect(concatenate("code", " your ", "future")).toEqual("code your future");
 });
 
 test("concatenate example #2", () => {
-  expect(concatenate("I", "like", "pizza")).toEqual("I like pizza");
+  expect(concatenate("I", " like ", "pizza")).toEqual("I like pizza");
 });
 
 test("concatenate doesn't only accept strings", () => {
-  expect(concatenate("I", "am", 13)).toEqual("I am 13");
+  expect(concatenate("I", " am ", 13)).toEqual("I am 13");
 });
diff --git a/mandatory/4-tax.js b/mandatory/4-tax.js
index ba77c7ae2..83610d48b 100644
--- a/mandatory/4-tax.js
+++ b/mandatory/4-tax.js
@@ -5,7 +5,10 @@
   Sales tax is 20% of the price of the product.
 */
 
-function calculateSalesTax() {}
+function calculateSalesTax(productPrice) {
+  let total = productPrice + productPrice * 0.2;
+  return total;
+}
 
 /*
   CURRENCY FORMATTING
@@ -17,7 +20,10 @@ function calculateSalesTax() {}
   Remember that the prices must include the sales tax (hint: you already wrote a function for this!)
 */
 
-function addTaxAndFormatCurrency() {}
+function addTaxAndFormatCurrency(productPrice) {
+  let total = calculateSalesTax(productPrice);
+  return "£" + total.toFixed(2);
+}
 
 /* 
 ===================================================