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.
['1821', '6647', '2509', 'n', 't', 'X', 'X', 'v', 'y', '6799', '2009', 'I', '2945', '5033', '1259', '227', '5429', 'l']