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.
['3853', 'U', 'Q', '2605', 'H', '7761', 'K', '4949', '5057', '1787', 'J', '7119', 'o', '1733', '9899', 'V', 'a', 'F', '833']