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.
['8557', 'V', '5933', '6647', 'r', '6817', '6535', 'q', 'w', '7251', 'g', 'v', 'y', '5211', 'i', '5765', '893', 'W', '7511', '787']