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.
['4235', 'V', 'b', '9131', '9081', '2619', '2331', 'N', 'u', '2543', 'L', 'M', '4827', 'k', '9421', 'a', 'Q', 'j']