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.
['3403', 'N', 'T', '3271', 'x', '8601', 'w', 'x', '7277', '2429', '6551', 'S', 'U', '3705', '8927', 'N', 'C', 'n', '4219']