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.
['7321', '6235', 'e', '1537', 'G', 'D', 'G', '7151', '8035', '8039', 'Y', 'C', '6577', 'q', '7187', '4193', '987', 'E', '4721', 'S']