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.
['8673', 'R', '7399', 'h', 'g', '177', 'C', 'b', '7181', 'm', '5715', 'x', '2715', '3853', 'b', '1681', '1445', 'S', '109', 'r']