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', 'z', '5901', 'm', 'd', 'g', 'f', '7843', '155', '5669', 'e', 'm', 'Z', 'R', 'D', 'l', 'k', '467', '5879', '2597']