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.
['h', '2573', '1547', '9997', 'i', '2509', 'U', 'f', 'y', '4871', 'F', 'w', '7641', '3437', '5627', 'i', 'm', 'x', 'k']