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.
['6601', '8237', 'v', '1669', '4899', '1939', 'c', 'c', '8587', '3113', 'S', '3403', '3239', 'u', '4215', '8457', '1503', 'k', 'o']