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.
['3307', 'y', '6813', 'E', '551', 'S', 'm', '6347', 'y', 'b', 'a', '469', '6799', '1765', 'M', '2997', '1685', '2513', '6507', '8793']