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.
['877', '6999', 'f', '5849', '5921', 'n', '2659', 'B', 'Y', 'c', 'g', '443', '9393', '6601', 'Z', '87', 'u', '2405']