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.
['Y', '9495', 'b', 'F', 'S', '5943', '8921', '1729', 'G', 'Y', '3789', '3925', '815', '8499', '4009', '7911', '8139', '3057', 'q']