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.
['K', '5519', '229', 'p', 'w', '1241', 'T', '6921', 'F', 'S', '7715', 'j', '3291', 'F', '5419', '2441', 'L', '1853']