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.
['G', '8673', 'S', 'A', 'S', 'k', '8977', '3231', '1579', 'T', 'p', '4251', '8767', '7251', '7193', '6929', 'A', 'k', '9685']