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.
['2539', 'c', '7115', 'N', '8293', 'F', '5991', '7743', 'r', 'm', '7963', '7249', 'P', '5923', '6605', 'o', 'M', '4369', '2229', 'f']