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.
['c', 'x', '6001', 'p', '497', 'm', 'x', 'D', '1543', 'c', 'L', '3459', '3453', 'L', 'A', 'C', '8715', 'N', '9381']