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.
['m', '2519', 'J', '169', 'K', 'm', '4887', 'c', '17', '3057', '5053', 'u', '4019', '9123', 'n', 'Y', 'Z', '3797', 'p']