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.
['7877', '3011', '6929', 's', 'K', 'V', 'J', '5567', '8241', '2605', '2317', 'c', 'U', '8467', 'M', '2607', '8995', 'C', '2605']