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.
['i', '8501', 'X', 'R', 'v', 'n', 't', '4489', 'i', 'i', 'w', '2611', '6395', 'z', '6747', '5397', '1797', '3351']