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.
['n', 'G', '5059', '8343', '8673', 'P', 'N', '5485', '2279', '6121', 'i', 'U', '7277', '8701', 'A', 'b', 'Z', 'R', '6371', 'G']