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.
['4787', 'J', '8889', 'G', 'i', 'A', 'u', '6943', 'H', '9687', 'y', '7821', 'e', 'G', 'd', '435', '1529', '8189']