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.
['O', '7791', '1019', '2755', 'b', 'A', '5137', 'j', '4359', '7753', 'X', '2473', 'G', 'g', '9575', '2777', '3925', 'E', '7959', 'x']