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.
['1431', 'F', '9545', '9515', 'a', '8121', '6591', '6003', '5477', '6279', '3777', '1493', '935', 'g', '9439', '7715', 't', '5719', 'r', 'o']