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.
['905', '1129', 'N', '8265', '4761', '649', 'N', '2071', '6151', '2329', 'h', '675', '4453', '6897', '6259', 'u', '1491', '8647', '3603', 'w']