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.
['6847', '2773', 'r', '1977', '8887', '8001', '6071', '9953', '4755', 'J', 'L', '5689', 'm', '2173', '4639', 'Y', '8501', '1099']