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', '619', '4453', 'n', 'u', 'l', 'L', '3913', 'H', 'b', 'J', 'w', '6763', 'q', '5325', '8771', 'u', 'Y', 'x', 'J']