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.
['P', 'n', 'q', '8871', '4283', '6379', 'F', 'E', '9391', 'E', 'u', 'Z', 'T', '5211', 'Z', 'u', '6157', 'n']