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.
['1179', '5855', '8115', 'R', '1337', 'G', 'z', 'k', '9475', 'Y', '3517', '5729', 'C', '7717', '7219', '1987', 'C']