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.
['J', '3129', 'l', '935', 'w', 'G', 'D', 'X', '5449', '3835', '9733', '6549', 'v', '7661', 'Y', 'L', 'h', 'Y', '881']