diff --git a/extra/1-currency-conversion.js b/extra/1-currency-conversion.js
index 75b3c6aab..7e562cdb0 100644
--- a/extra/1-currency-conversion.js
+++ b/extra/1-currency-conversion.js
@@ -5,7 +5,12 @@
   Write a function that converts a price to USD (exchange rate is 1.4 $ to £)
 */
 
-function convertToUSD() {}
+function convertToUSD(price) {
+  return price * 1.4;
+  
+
+
+}
 
 /*
   CURRENCY CONVERSION
@@ -14,8 +19,13 @@ function convertToUSD() {}
   Write a new function for converting to the Brazilian real (exchange rate is 5.7 BRL to £)
   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(price){
+  
+  let priceAfterFee = price * 0.99;
+  let priceInBRL = priceAfterFee * 5.7;
+  return Math.round(priceInBRL * 100) / 100;
+  }
 
-function convertToBRL() {}
 
 /* ======= 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..e13bdfaed 100644
--- a/extra/2-piping.js
+++ b/extra/2-piping.js
@@ -16,26 +16,33 @@
   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;
+let startingValue = 2;
 
 // Why can this code be seen as bad practice? Comment your answer.
-let badCode =
+let badCode =  format(multiply(add(startingValue, 10), 2));
+
 
 /* BETTER PRACTICE */
+let valueAfterAddition = add(startingValue, 10); // 12
+let valueAfterMultiplication = multiply(valueAfterAddition, 2); //12*2
+
+let goodCode = format(valueAfterMultiplication);   
+
 
-let goodCode =
 
 /* ======= 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..e6983c6cc 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 "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;
+  const 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 9eb8c8cd7..717facfdb 100644
--- a/mandatory/2-logic-error.js
+++ b/mandatory/2-logic-error.js
@@ -1,16 +1,16 @@
 // 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..f3ddfa3a7 100644
--- a/mandatory/3-function-output.js
+++ b/mandatory/3-function-output.js
@@ -1,18 +1,23 @@
 // Add comments to explain what this function does. You're meant to use Google!
+// we use math.random when we want a random floating point number between 0 and 10.
 function getRandomNumber() {
   return Math.random() * 10;
 }
 
 // Add comments to explain what this function does. You're meant to use Google!
+// The concat() method joins two or more strings, in this example there is no space between the words, when we want to put space between words we should put quetation 
+//example word1.concat(" ", word2);
 function combine2Words(word1, word2) {
   return word1.concat(word2);
 }
 
 function concatenate(firstWord, secondWord, thirdWord) {
+  return firstWord.concat(" ", 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.
 }
 
+
 /* 
 ===================================================
 ======= TESTS - DO NOT MODIFY BELOW THIS LINE =====
diff --git a/mandatory/4-tax.js b/mandatory/4-tax.js
index ba77c7ae2..0ba3487cd 100644
--- a/mandatory/4-tax.js
+++ b/mandatory/4-tax.js
@@ -5,7 +5,11 @@
   Sales tax is 20% of the price of the product.
 */
 
-function calculateSalesTax() {}
+function calculateSalesTax(price) {
+  const salesTax = 0.2 * price; 
+    const totalPrice = salesTax + price;
+  return totalPrice;
+}
 
 /*
   CURRENCY FORMATTING
@@ -17,7 +21,11 @@ function calculateSalesTax() {}
   Remember that the prices must include the sales tax (hint: you already wrote a function for this!)
 */
 
-function addTaxAndFormatCurrency() {}
+function addTaxAndFormatCurrency(price) {
+  const totalPrice = calculateSalesTax(price);
+
+  return "£" + totalPrice.toFixed(2);
+}
 
 /* 
 ===================================================