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.
['4421', '7931', '1285', 'M', '7241', '7763', 'l', '6001', 'i', 'L', '7793', '2013', '8763', 'U', '5249', 'O', '473', '9811']