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.
['4437', '1265', '1519', 'K', 'Q', 'b', 'n', 'J', '6631', 'K', 'q', 'D', 'U', 'u', '3653', '5169', 'L', 's']