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.
['9319', 'e', '991', '4719', '579', '1315', '5969', 'r', 'K', '3171', 'U', 'L', 'H', '6967', '5221', '2325', '1191', 'u', '9999', '2803']