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.
['7829', 'V', 'L', '3201', '8147', 'm', 'e', 'P', '6991', '8157', 'p', 'X', '5111', 'T', 'b', '3509', '6777', 's', '5831', 'z']