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.
['X', 'f', 'q', '4665', '1853', '7613', '4137', 'x', 'P', '1693', 'J', '7599', '5687', 'u', '3809', '4723', '3935', 'M']