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.
['7991', '2305', '2053', '6519', '9065', 'l', 'c', '1283', 'k', 'Z', 'V', '1901', 'b', '7449', 'r', '9513', '7873']