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.
['Z', '7939', 'N', '1135', '4495', 'a', 'v', '1767', '7739', '3443', 'o', 'b', 'Z', 'B', 'L', 'e', '9071', '9787']