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.
['3397', '1937', 'f', 'G', '8253', 'E', 'K', 's', '9209', 'R', 'a', 'f', '2439', '1691', '1081', '4879', '3279', 'Z', '4497', '9617']