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.
['4811', 'Q', '2289', 'N', 'I', '7681', 'z', '8179', '3359', '5299', 'R', 'z', '8697', '5781', '4803', '2715', '6511', '1371']