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.
['9341', '6649', 'q', 'R', 'r', '6003', 'J', 'P', 'G', '7903', '1007', '4231', 'D', 'm', 'A', '5577', 'f', '6461', 'n']