Add challenge submission links

Author: DarshalShetty

index.md

@@ -139,7 +139,7 @@ Aug. 26 | [Introduction](https://docs.google.com/presentation/d/13jmEAwqD7naNAj0
 Aug. 28 | [From Lvar to x86](https://docs.google.com/presentation/d/1KUlWTAvdcKtZNOST9ITpmiOe34lD2DFsycH5oT2oMuU/edit?usp=sharing) |
 Sep. 2 | Example Compilation from Lvar to x86 in [Racket](./example-var-73.md) and [Python](./python-var-73.md) |
 Sep. 4 | [Register Allocation, Introduction and Liveness](https://docs.google.com/presentation/d/1jL4M6G6DDnfqOPsCab9_6k7PcV_wRBd4p9Xn2LzobOE/edit?usp=sharing) |
-Sep. 9 | [Register Allocation: graph coloring](https://docs.google.com/presentation/d/1qPKUGZnqh6ggfP5_emHVJhSTyPRI0iD02jRTdB9mbwo/edit?usp=sharing) | Integers and Variables, submit in [Racket](https://autograder.luddy.indiana.edu/web/project/1913) or [Python](https://autograder.luddy.indiana.edu/web/project/1912)
+Sep. 9 | [Register Allocation: graph coloring](https://docs.google.com/presentation/d/1qPKUGZnqh6ggfP5_emHVJhSTyPRI0iD02jRTdB9mbwo/edit?usp=sharing) | Integers and Variables, submit in [Racket](https://autograder.luddy.indiana.edu/web/project/1913) or [Python](https://autograder.luddy.indiana.edu/web/project/1912) (see also, [Racket challenge](https://autograder.luddy.indiana.edu/web/project/1950) [Python challenge](https://autograder.luddy.indiana.edu/web/project/1949))
 Sep. 11 | Code Review: Integers and Variables
 Sep. 16 | [L_If language, type checking, and x86_If](https://docs.google.com/presentation/d/1ZJWJN8mAPS3NpTBkbkY8xauZtIGbZdCwTovtN1a4gUo/edit?usp=sharing) | Integers and Variables, late deadline
 Sep. 18 | [Conditionals and Explicate Control](https://docs.google.com/presentation/d/1OALjNzmyLNt_Yg3eV_xjLx7ZxQ_8q2fLLi0I9nJjX9I/edit?usp=sharing)