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.
['b', 'D', 'b', 'X', '7971', '4749', 'T', 'S', '6701', 'y', 'Q', '9933', 'X', '7713', '3003', '9473', 'J', '7391', 'q', 'L']