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.
['8559', '8137', '4927', 'W', 's', 'h', 't', '6219', '3427', 'Q', 'L', '5345', '4361', '1681', '6147', '63', '2039', '5949', '1539']