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.
['9703', '3313', 'Z', '7651', 'L', 'Z', '4731', 't', '73', '7521', 'o', '6091', 'x', '5593', 'e', 'B', 'b', '8757', '8475', 'R']