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.
['D', 'Z', '6195', 'J', 'a', 'C', '4473', 'Z', '843', '8669', '9617', '3849', 'f', '8335', 'U', '5687', 'o', '8779', '7509']