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.
['o', 'T', '731', 'r', '6403', 'U', '2173', 'w', 'C', 't', '2109', 'F', '4395', 't', 's', '235', 'W', '2853', 'w']