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.
['M', '1589', '8353', 'X', 'P', '3173', 'V', '1335', 'm', 'l', '6421', '4823', 'r', '8941', '4255', '9107', 'z', '2449', '2321', 'l']