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.
['J', 'v', 'P', 'k', 'y', 'k', '5337', '2783', 'I', 'V', '8873', 'G', 'C', 'I', '4785', '6783', 'P', '2683', 's']