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', 'n', 'y', 'p', '7875', '7975', 'h', '7981', 'K', '169', '5471', '9139', 'N', 'M', 'p', '835', '9535', 'V', 'V', '7499']