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.
['V', 'W', '2139', '5433', 'N', '1019', '2409', '4713', '3831', '3419', '627', '6741', 'k', '9', '8839', '6045', '6799', '775', 'F', 'n']