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.
['2453', 'x', '3595', '7281', 'n', '1613', 'q', '4747', 'K', 'C', 'D', '5511', '7739', '7955', 'b', '555', 'V', 'G', '4807']