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.
['6247', '5719', '6555', '7509', 'g', 'd', 'I', 'h', 'n', '1903', 'Z', '8643', '2049', 'U', '4429', 'X', 'j', 'b']