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.
['f', '3693', '5337', '2639', 'k', '651', 's', 'i', '391', 'R', '9579', '3007', '8187', 'a', 'g', '929', '9335', '5979', '5455']