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.
['y', 'c', 'U', '4831', '3413', 'J', 'b', 'n', 'P', '449', 'l', 'd', 'w', 'q', 'U', '4031', 'N', '257', '3295']