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.
['s', '6979', '5225', '2165', '9457', '6243', '6033', 'L', '6233', '6419', 'o', 'k', '6219', 'f', 'C', '6669', 'X', 'C', '6329', '5831']