In this task, you are given an input list A. You need to find all the elements of the list that are numbers and calculate their sum.
['9507', 'W', 'g', 'k', '5191', '2597', 'S', '2145', 'X', 'n', '6537', 'K', 'l', '8133', '6263', '885', '969', 'f', '5021', 'i']