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.
['G', 'h', '8647', '7635', 'h', 'x', 'R', '1677', 'k', 'c', '2331', '6277', 'v', 'b', '5971', '4901', 'w', '7437']