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.
['S', '2877', 'X', '4039', '661', '6371', '4977', '9483', '9829', '3063', '7337', '8051', 'f', 'y', 'j', '2019', '5129', '8457', '509', '7507']