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.
['4285', '1489', '9439', '8237', '4661', '3015', '2361', '7631', 't', 'A', '1697', 'H', '3601', '5399', 'J', '9233', '9157', 'H', 'Y', '1449']