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.
['g', '9447', 'P', '8443', '1727', 'R', 's', '4291', 'x', 'p', '1275', 'i', 'v', '6575', 'K', '21', '121', 'y']