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.
['5201', 'V', '205', 'Z', 'o', 'A', 'U', '9705', 'n', 'm', '1589', 'n', '8251', '3261', '2709', 'O', 'f', '7699']