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.
['4699', 'U', '2399', 'z', 'y', '7107', 'i', 'h', 'O', 'u', 'k', '6831', '8585', '8945', 'u', 'B', '6073']