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.
['Z', '9161', '6629', '5345', 'r', 'O', 'r', '7959', 'f', '5499', 's', 'N', '6787', '9391', '8033', '5395', 'z', '7487', 'R', 'c']