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.
['M', '2045', '5625', 'f', '5117', '1535', '1335', 't', '985', '5987', 'l', 'Q', '6737', 'Y', '8291', 'D', 'y', '1887', '3315']