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.
['Q', 's', '6889', 'L', '8767', 'N', 'P', 'w', '5023', 'R', '8491', 's', 'Y', '5479', 'T', '3781', 'M', 'V']