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.
['y', '1237', 'Z', 'v', 'C', 'F', '3793', 'h', 'R', 'j', 'S', '4215', '57', '8493', 'W', 'b', 'Z', 'L']