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.
['r', '2605', 'M', '6447', '7799', 'M', 'T', '8097', '8457', '9031', '5383', 'P', '3117', 'y', 'W', '3199', '8671', 'o']