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.
['5915', '5301', 'J', 'L', '7471', '6681', '3721', '5765', '1507', '529', '4373', 'C', 'Y', '2885', '5973', '7131', 'S', '2531', 'I', 'L']