diff --git a/extra/1-currency-conversion.js b/extra/1-currency-conversion.js
index 75b3c6aab..0c925ab2c 100644
--- a/extra/1-currency-conversion.js
+++ b/extra/1-currency-conversion.js
@@ -5,8 +5,12 @@
   Write a function that converts a price to USD (exchange rate is 1.4 $ to £)
 */
 
-function convertToUSD() {}
+function convertToUSD(priceInGBP) {
+  const exchangeRate = 1.4;
+  const priceInUSD = priceInGBP * exchangeRate;
 
+  return `$ ${priceInUSD.toFixed(2)}`;
+}
 /*
   CURRENCY CONVERSION
   ===================
@@ -15,7 +19,13 @@ 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(amountInGBP) {
+  const exchangeRate = 5.7;
+  const transactionFee = 0.99; 
+  const amountInBRL = amountInGBP * exchangeRate * transactionFee;
+
+  return `R$ ${amountInBRL.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..4f30e32ab 100644
--- a/extra/2-piping.js
+++ b/extra/2-piping.js
@@ -16,26 +16,28 @@
   the final result to the variable goodCode
 */
 
-function add() {
-
+function add(num1, num2) {
+  return num1 + num2;
 }
 
-function multiply() {
-
+function multiply(num1, num2) {
+  return num1 * num2;
 }
 
-function format() {
-
+function format(amount) {
+  return `£${amount}`;
 }
 
 const startingValue = 2;
 
 // Why can this code be seen as bad practice? Comment your answer.
 let badCode =
+//It's a constant, so it cannot be changed. 
 
 /* BETTER PRACTICE */
 
-let goodCode =
+//let goodCode =
+let myStartingValue = 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/mandatory/1-syntax-errors.js b/mandatory/1-syntax-errors.js
index d9e004465..1dab4c400 100644
--- a/mandatory/1-syntax-errors.js
+++ b/mandatory/1-syntax-errors.js
@@ -1,14 +1,14 @@
 // 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 "and I am $age years old`;
+  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";
 }
diff --git a/mandatory/2-logic-error.js b/mandatory/2-logic-error.js
index 9eb8c8cd7..d7eab5cb3 100644
--- a/mandatory/2-logic-error.js
+++ b/mandatory/2-logic-error.js
@@ -1,16 +1,15 @@
 // The syntax for these functions is valid but there are some errors, find them and fix them
 
 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..4a3ef1f7c 100644
--- a/mandatory/3-function-output.js
+++ b/mandatory/3-function-output.js
@@ -2,16 +2,18 @@
 function getRandomNumber() {
   return Math.random() * 10;
 }
+// This function gets a random number below 1 and multiplies it by 10.
 
 // Add comments to explain what this function does. You're meant to use Google!
 function combine2Words(word1, word2) {
   return word1.concat(word2);
 }
+// This brings together the two string; word1 and word2.
 
 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.
+  return '${firstWord}${secondWord}${thirdWord}';
 }
+//This could also be written as firstWord.concat(secondWord, thirdWord);
 
 /* 
 ===================================================
diff --git a/mandatory/4-tax.js b/mandatory/4-tax.js
index ba77c7ae2..48ef0b1bf 100644
--- a/mandatory/4-tax.js
+++ b/mandatory/4-tax.js
@@ -5,7 +5,14 @@
   Sales tax is 20% of the price of the product.
 */
 
-function calculateSalesTax() {}
+function calculateSalesTax(price) {
+  let price = number;
+  let percentage = 0.2; 
+  const currency = "£";
+  let taxAmount = price * percentage;
+  let totalPrice = price + taxAmount;
+  return `${currency}${totalPrice}`;
+}
 
 /*
   CURRENCY FORMATTING
@@ -17,7 +24,13 @@ function calculateSalesTax() {}
   Remember that the prices must include the sales tax (hint: you already wrote a function for this!)
 */
 
-function addTaxAndFormatCurrency() {}
+function addTaxAndFormatCurrency(number) {
+  let price = number;
+  let percentage = 0.2; 
+  const currency = "£";
+  let taxAmount = price * percentage;
+  let totalPrice = price + taxAmount;
+  return `${currency}${totalPrice.toFixed(2)}`}
 
 /* 
 ===================================================