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.
['8717', '5437', 'l', '8573', 'r', 'k', 'B', 'w', '4123', '4471', '5169', 'D', '3975', '6581', 'z', '41', 'X', '5057', 'i', '8153']