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.
['g', '7903', '2653', 'c', '425', 'z', 'I', '1997', '617', 'i', '9009', '9917', '6993', '3517', 'M', '8237', '8027', 't', 'R']