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.
['955', 'b', 'x', 'q', 'e', 'i', 'n', 'm', 'P', '4325', '4273', '1455', 'u', 'C', 'T', 'P', '857', 'l', 't', '9453']