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.
['8159', '5353', '3413', '6243', 'M', '4137', '2429', '9357', '1283', 'D', '1429', '2475', '9157', 'H', 'u', '7049', '3821', '7091']