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.
['g', 'A', 'r', '539', '5459', '2725', '7447', '3693', '1757', 'r', 'W', '5949', '4569', '5153', '3985', 'Q', '505', 'M', '8989']