can you help me with the extra credit part?

The most common letter is E with 147 occurences. The least common letter is J with 0 occurences. Extra Credit ( 10 Points) Enhance the program so if there is a tie for the most (or least or both) common letter, the program displays all of the letters that are tied. So for this input, the output would look like - The most common letter is E with 147 occurences. The least common letters are J,X with 0 occurences