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.
['3179', 'J', '7343', '2221', '103', '3975', 'y', 'M', '6409', '1961', 'F', '7689', '8575', '9591', 'b', '4217', 'W', 'N', 'D', 'i']