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.
['f', '5987', 'n', 'K', '3925', '8921', '2889', '6181', 'z', '4587', 'v', 'q', '1431', 'c', '911', 'w', 'a', '6261', 'x', '8459']