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.
['a', '4255', 'K', 'o', '9637', 'K', 'N', 'W', '8691', 'k', '9233', 'r', 'Q', 'h', '7997', '9465', '9345', 'B', 'C', '2937']