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.
['1715', 'p', 'e', '6967', '6641', 'W', '6267', '8653', 'R', '1687', '8913', 'N', 'f', 's', 'b', '3373', '3931', '6699']