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.
['W', 'U', '2133', '8801', 'P', 'O', 'e', '527', '8903', 'W', 'g', '7579', 'o', 'j', 'Z', '6607', '8931', 'Y']