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.
['4517', '9581', 't', '1989', 'R', '9659', '6955', 'h', 'X', 'a', 'j', '3961', 'y', '2619', 'j', 'P', 's', '7871', 'W', '5355']