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.
['9905', 'm', 'Q', 'S', 'T', '7821', '1773', '9515', '3963', '2931', '7023', '8677', '1739', 'O', '909', '9153', '8319', 'k', '2851']