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.
['6155', '783', '3725', 'L', 'Y', 'U', 'u', '5635', '1967', '4851', '1251', '9773', 'K', '1391', 'p', '5035', '6405', '5041', 'h']