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.
['39', '3059', '2925', 'i', 'I', '7935', '4777', '3341', '5759', 'q', '9935', 'x', '6979', 't', '7439', '8569', '7973', '2421', 'Y']