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.
['W', '9225', 'W', '3467', '9685', 'n', '6617', 'O', '9225', '4637', '3223', 'm', 'I', 'E', 'T', '5363', '4229', '3991', 'u']