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.
['5331', '1083', '3081', 'r', '9117', '1157', 'm', '6195', 'a', '3335', '5743', 'f', 'F', 'X', 'B', '6315', '3081', '3449', 'f', 'S']