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.
['2173', '2551', '797', 'h', '5943', 'H', 'I', 'A', 'U', 'W', 'm', 'W', '9143', 'r', '7799', '3895', 'G', 'D', '4013']