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.
['4257', '2401', '6439', 'G', 'D', '9427', 'u', '9937', 'J', '4719', 'C', 'd', '4977', '7257', '5883', '5443', '7149', 'X', '2253', 'c']