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.
['P', '7709', 'E', '4737', 'J', '5819', '5231', '6291', 'T', 'm', '7725', '3161', 'o', 'x', 'D', 'H', 'l', '3717']