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.
['5857', '1523', '5035', 'B', 'D', 'G', 'E', '5399', 'N', 'Y', '4977', 'R', '5813', 'i', '7733', '8113', 'I', 'z', 'x']