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.
['D', '3225', '4485', '6795', 'D', 'N', 'w', '5019', '6411', '9369', 'q', '445', 'x', '637', 'P', 'L', 'k', 'b', 'c']