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.
['8801', '4271', 'l', '2873', '5703', 'v', '3379', 'T', '3909', 'U', 'C', '3445', 'R', 'x', 'G', '2251', 'c', '6221', '7477']