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.
['U', '1301', '7431', '8217', '6019', 'B', '4221', '2663', 'N', 'k', '6837', '8805', 'F', '369', 'd', '2277', '6815', 's']