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.
['z', '5211', '893', 'L', 'L', 'a', '6557', '4203', 'Z', '2497', '2745', 'q', 'Y', '7321', '5935', '4573', 't', 'B']