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.
['v', 'w', '3139', 'c', 'f', 'X', '8707', 'z', '7071', '937', '5573', '5157', 'f', '6901', 'P', 'D', '7497', '915', '933', '2431']