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.
['5411', '9789', 'P', 'E', 'Y', 'u', '7559', 'B', 'q', '5405', 'H', 'q', '7853', 'w', '3605', 'N', 'U', '8131']