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.
['V', '1743', 'r', '6513', '7631', '3011', '4579', 'r', 'i', '4399', '1491', 'm', 'f', 't', 'm', '5493', 't', '4385', 'N']