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.
['k', '1489', 'x', '6543', 'I', 'l', 'D', '6299', '1473', 'a', '7661', 'z', 'E', 'Z', 'U', '3671', '2873', 'e', 'p']