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.
['1833', 'K', 'G', '8611', '6341', 'b', '2725', '2613', '7883', 'q', 'j', '5163', '5421', 'J', 'c', 'N', 'l', 'f']