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.
['N', '8533', 'w', 'G', '9251', '7195', 'i', '5009', 'Z', '8553', '7385', 'C', '4513', '9303', '6615', 'b', '2949', '7833', 'U']