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.
['B', '6607', '6735', '3125', '6025', 'u', '6861', '2391', 'y', 'Y', '2789', 'x', '7707', 'J', '6105', 'F', '5199', 'G', '7721', 's']