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.
['9675', 'U', 'R', '6567', '4703', '9831', '4189', 'U', 'z', '6763', 'v', 'N', '5917', '7185', 'k', '1713', '3951', 'T', 'S', '1877']