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.
['7503', '4903', '6255', 'f', '6847', 'Z', '1403', 'X', '2745', '8743', '6913', '4897', 'M', '5037', '1579', 'I', 'o']