Definition: In this task, you are given an input list A. You need to convert all the alphabets in the list with a number representing their position in the English alphabet. E.g., replace A by 1, B by 2, a by 1, b by 2, and so on.
Input: ['1107', 'C', '5921', '7815', '1509', 'l']

1107, 3, 5921, 7815, 1509, 12