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.
['8821', '6899', 'S', '5881', 'U', '2489', 'X', 'd', '6835', '7215', 'F', '1143', '4871', '4729', '9761', 'g', 'W', '353', '9059']