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.
['D', 'h', 'W', 'B', 'N', '115', 't', 'I', 'E', 'P', 'l', 'K', '6501', '3159', 'K', 'x', 'n', '3621', 'f']