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.
['2875', 't', '5051', '115', '7889', '4101', 'X', 'O', 'L', '2245', '3307', 'K', '441', '6111', 'V', 'L', 'c', '6659', '7745', 'S']