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.
['6713', '6335', 'E', 'l', '7495', '1005', '475', 'O', '8941', '8387', '3915', 'r', 'j', 'x', 'M', 'W', 'H', '5715']