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.
['4131', 'T', 'x', '9493', 'j', 'w', 'L', 'w', '4627', 'E', '8239', '7317', 'z', '781', '7489', '7647', '4863', '3331', '9975', '4805']