The function f(x) takes a string as input and performs the following operations:
1. Reverse the input string.
2. Convert all lowercase letters in the reversed string to uppercase.
3. Replace all instances of the letter 'a' (both lowercase and uppercase) with the symbol '@'.
4. Replace all instances of the letter 'e' (both lowercase and uppercase) with the symbol '3'.
5. If a character in the reversed string is a digit (0-9), double its value.

