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.
['K', '4477', '5207', 'l', '6243', 'T', 'r', 'v', '7087', 'R', 'K', 'T', 'I', 'z', 'c', '1965', 'W', '3557', 'm']