diff --git a/readme13-15.md b/readme13-15.md
index 11bc51a..c506ad8 100644
--- a/readme13-15.md
+++ b/readme13-15.md
@@ -145,7 +145,7 @@ two_power_of_five = power(2)(5) # 32
 1. Flatten the following list of lists of lists to a one dimensional list :
 
    ```py
-   matrix=[[[1, 2, 3]], [[4, 5, 6]], [[7, 8, 9]]]
+   list_of_lists =[[[1, 2, 3]], [[4, 5, 6]], [[7, 8, 9]]]
 
    output
    [1, 2, 3, 4, 5, 6, 7, 8, 9]
@@ -180,7 +180,13 @@ two_power_of_five = power(2)(5) # 32
    {'country': 'SWEDEN', 'city': 'STOCKHOLM'},
    {'country': 'NORWAY', 'city': 'OSLO'}]
    ```
-4. Write a lambda function which can solve slope or y-intercept. 
+4. Change the following list of lists to flat list:
+   ```py
+   names = [[('Asabeneh', 'Yetaeyeh')], [('David', 'Smith')], [('Donald', 'Trump')], [('Bill', 'Gates')]]
+   output
+   ['Asabeneh Yetaeyeh', 'David Smith', 'Donald Trump', 'Bill Gates']
+   ```
+5. Write a lambda function which can solve slope or y-intercept. 
 
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