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.
['Q', '6217', 'e', 'R', '7009', '137', 'v', '957', 'F', '9479', 'K', '7313', 'F', 'U', '2557', 'g', 'J', 'P', '3977']