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.
['J', 'Y', '6549', '9301', '8769', '4295', '5935', 'E', 'C', '1771', '4313', 'u', '8683', '9211', 'P', 'k', '7709', 'X']