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.
['y', '7691', 'f', 'g', 'd', '4101', '6291', 'K', '1545', '2121', '7911', '9145', 's', 'P', 'M', 'V', '4333', '9171']