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.
['S', '8641', '5343', '447', '2313', '7151', '3071', '8923', 'U', '8113', 'I', 'j', 'C', 'K', 'D', 'S', '9815', 'q', '1683', '8311']