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', '8081', '8431', '4325', 'Z', 'K', '9015', '4145', 'L', 'o', '989', 'i', 'M', '5909', 'V', 'z', '8643', '7559', 'M', '8097']