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.
['4175', '6869', 'S', 'T', 'd', '109', 'r', '2565', '5327', 'n', '21', 'd', 'q', 'a', '4421', 'S', '9835', 'W', '8875']