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.
['r', '649', '657', 't', 'D', '7665', 'N', '4723', 'E', 'I', 'k', '2021', 'b', '5123', '5067', '5789', '8527', '5295', 'h', '9939']