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.
['d', '1489', '883', '8821', 'a', '4479', 'N', 'k', '3515', 'm', '9963', 'T', '285', 'K', 'M', 'u', '4325', 'U']