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.
['1815', 'U', '869', 's', '1847', 'C', '2711', 'S', 'i', '7949', '4477', '5093', 'D', '8661', '3835', '4087', '73', 'V', '3149', 's']