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.
['w', 'U', 'o', '891', 'k', 'O', '2747', '4891', 'Y', '3563', '5205', 'o', 'o', '871', 'f', 'J', '3271', '759']