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.
['g', 't', 'J', '4029', 'U', '5493', 'p', 'G', '2977', 't', '7785', '8581', '7937', '7727', 'O', 'h', 'f', '8913']