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.
['3599', 'a', '181', '3315', 'T', '6841', '9183', 'W', 'q', 'h', '2081', '4257', '709', '9763', '5093', 'r', '6799', '1765', '5181']