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.
['O', '4661', 'F', 'l', '747', '5019', '5101', 'M', '5009', '4875', '6873', '9893', 'W', 'l', 'l', '881', '7503', '4351', 'G', 'S']