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.
['1497', '6991', 'O', '4795', '8541', '7451', 'l', '709', '6111', 'F', 'k', '7151', '7917', 'O', '7301', '2711', '6015', '4297']