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.
['4483', '9929', '2829', 'X', 'r', 'i', '2947', 'w', '2361', 'L', 'N', 'D', '3711', 'q', 'm', 'z', '8789', 'l', '5157', '3171']