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.
['h', '6937', 'U', 'f', 'S', 'm', '9699', 'E', '4559', 'p', 'Z', 'o', '6409', 's', '4537', '5135', '6901', '6489', '5833', 'l']