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.
['A', 'W', '4439', '4345', 'j', '8247', 'X', 's', '6717', 'c', '1319', 'Q', 'm', '5931', '425', '6903', '1141', 'U']