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.
['783', '1293', 'C', 'g', 'J', '5347', '6785', 'N', 'L', 'y', '7847', 'J', 'X', 'm', 'Z', '9535', '4671', 'K', '9517']