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', 'y', 'K', '2091', '8035', 'j', '7957', 'w', '525', 'A', '7981', '9101', '1941', '7435', 'j', '2875', 'z', '4431', '5713']