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.
['J', '2447', 'R', 'M', 'R', '3201', '2335', 's', 'u', '6225', 'l', '7671', 'd', 'n', '1129', 's', '3011', '5313', '2291', 'l']