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.
['x', 'd', '5121', 'I', '6737', '3789', '6167', 'C', '8947', 'k', '4715', '1885', 'H', 'B', '5685', 'S', '4615', 's', '7709']