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.
['L', 'k', '8661', 'Y', '4229', '1229', '7035', 'z', 'M', '8709', 'R', 'X', 'w', 'y', '6165', '6099', '7639', 'T']