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', 'B', '6763', 'L', '2109', 'm', 'q', '5561', '837', '747', '511', '1623', '4603', '3263', '3849', 'I', '7507', '7191', 'k', 'z']