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.
['6533', '7343', 'K', '7827', 'I', '5135', '9381', 'c', 'x', 'b', '1493', '603', '5317', 'j', '6967', 'U', 'O', '3911', '7823']