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.
['C', '3351', 'h', 'P', '7215', 'D', '1099', 'O', 'K', 'G', 'i', '3873', 'u', '8221', '2221', '4989', '355', '689']