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.
['7111', '7139', 'N', 'Y', '2229', 'b', 'S', '2925', '7117', '4741', '4941', '3033', 'R', 'u', 'i', '5551', 'j', '5899', 'l']