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.
['a', '2453', '7109', 'W', 'P', 'u', '6553', '2755', 'W', 'H', 'N', '5039', 'z', '1747', 'L', '1243', '7471', 'T', 'T', 'J']