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.
['z', 'U', '2251', '4335', 'n', 'O', '4075', '5299', 'd', '95', '3111', 'J', '6317', 'O', 'S', 'j', '5615', '6379', 'C']