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.
['f', '2123', '1623', 'F', '6555', '8155', 'M', 'L', '7805', 'K', '2025', 'F', 't', 'J', 'k', 'k', '4833', '2063', 'C']