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.
['5193', '7759', '7911', '6515', 'R', '8729', 't', '8323', 'A', 'I', '6747', '6871', 'A', 'h', 'f', '7281', '461', 'z', 'L']