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.
['5559', '5217', 'D', '5853', 'U', '5455', '2097', '4651', '7643', '7733', 'y', 'T', '2203', 'P', 'W', '4645', '8981']