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.
['2107', 'D', 'k', '4705', '4315', '7867', '3389', '4477', '1267', '8751', '2439', 'O', '6613', '725', '3621', 'q', 'l', 'o', 'K', '7417']