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.
['t', 'C', 'f', '5249', 's', 'r', 'd', 'F', '8531', '2115', 'K', 'N', 'i', 'R', '215', 'X', '9689', '1203']