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.
['K', '5791', '3415', '593', '1047', 'p', 'F', 'U', 'z', 'b', '497', '8635', '8639', 'A', '3025', 'r', '3241', 'r']