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.
['Q', 'D', 'd', '3195', 'I', 'i', '895', '7401', '491', '8939', 't', '845', '1317', 'E', '3279', 'Y', 'W', '933', '5461']