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.
['543', '8351', 'I', 'M', '6647', '731', 'b', 'r', 'l', '3935', 'k', 'z', 'v', '2131', '7781', 'X', '9419', '5013', 'F']