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.
['5551', 'f', '4937', 'z', 'X', '7945', 'I', 'u', '643', '4507', '3995', 's', 'a', '3935', 'T', '6173', '3561', '1427', '5567']