diff --git a/session-01/validators.js b/session-01/validators.js
index 56ea66d..49578a3 100644
--- a/session-01/validators.js
+++ b/session-01/validators.js
@@ -7,7 +7,35 @@
   - username cannot contain special characters
 */
 function validUsername(username) {
-  return;
+
+  let goodUsername = false;
+
+  // username must be between (and including) 3-10 characters in length
+  if(username.length >= 3 && username.length <= 10) {
+
+    // username must begin with a letter 
+    /*
+      /^[a-zA-Z]/ is the regex that test if a expression's first character is a letter
+    */ 
+    if(/^[a-zA-Z]/.test(username)) {
+
+      // username may contain numbers and letters
+      /*
+        /^[A-Za-z0-9]*$/ is the regex that test if a expression contains both number and letter
+      */
+      if (/^[A-Za-z0-9]*$/.test(username)) {
+
+        // username cannot contain special characters
+        /*
+          /[^a-zA-Z0-9]/ is the regex that test if a expression contains special character
+        */
+        if (!(/[^a-zA-Z0-9]/.test(username))) {
+          goodUsername = true; 
+        }
+      }
+    }
+  }
+  return goodUsername;
 }
 
 /*
@@ -17,7 +45,23 @@ function validUsername(username) {
   - password must contain at least 1 letter, 1 number, and 1 special character
 */
 function validPassword(password) {
-  return;
+  let goodPassword = false;
+
+    // password must contain at least 1 letter, 1 number, and 1 special character
+    /*
+      - [A-Za-z\d] Ensures that the first character is an alphabet or digit.
+      - [A-Za-z\d!@#$%^&*()_+]{7,19} will match minimum 7 maximum 19 character. This is required as he presceding character class 
+          would consume a single character making the total number of characters in the string as minimum 8 and maximum 20.
+      - $ Anchors the regex at the end of the string. Ensures that there is nothing following our valid password
+      - / at the beginning and end of regex tells the beginning and end of your regex expression
+    */
+
+    if (/^(?=.*[a-zA-Z])(?=.*\d)(?=.*[!@#$%^&*()_+])[A-Za-z\d][A-Za-z\d!@#$%^&*()_+]{9,63}$/.test(password)) {
+      goodPassword = true;  
+    }
+
+  return goodPassword;
 }
 
+// Test to see that git is working and is able to push to repo on github.
 module.exports = { validUsername, validPassword };
diff --git a/session-02/exercise.js b/session-02/exercise.js
index 6ade818..6131f3b 100644
--- a/session-02/exercise.js
+++ b/session-02/exercise.js
@@ -3,7 +3,15 @@
   For example, for the input ["cat", "hat"], return ["CAT", "HAT"]
 */
 function transformArrayToUpper(listOfStrings) {
-  return;
+
+  /*
+    - map() method: 使用 map() method 来创建一个 array by applying a function to each element of the array.
+    - word.toUpperCase(): 使用 .toUpperCase() 来转换到大写
+    - Arrow function: The arrow function word => word.toUpperCase() takes each string in the strings array and returns its .toUpperCase version.
+
+  */
+  const upperCase = listOfStrings.map(word => word.toUpperCase());
+  return upperCase;
 }
 
 /*
@@ -16,7 +24,24 @@ function transformArrayToUpper(listOfStrings) {
     the function should return 51
 */
 function sumOfAllAges(listOfStudentObjects) {
-  return;
+  // initializing ageTotal to keep track and add all ages
+  let ageTotal = 0;
+
+  //用 .forEach 来循环所有 element of object Array 里面的 age
+  listOfStudentObjects.forEach(ageFromElement => {
+
+    //用 if condition 来 omit 掉所有不符合的年龄 like empty age or 小于 0岁
+    if (ageFromElement.age >= 0) {
+
+      // 所有符合要求的年龄加到 ageTotal
+      ageTotal += ageFromElement.age;
+    }
+    // else {
+      // console.log("Age is invalid");
+    // }
+    });
+
+  return ageTotal; 
 }
 
 module.exports = { transformArrayToUpper, sumOfAllAges };