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.
['3877', 'A', '2623', '6855', '7407', 'Y', '857', '625', 'w', '9921', 'M', '3301', '9735', 'B', '4243', 't', 'e', 'I', '459']