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.
['P', 'X', 'u', 'B', 'G', 'P', 'C', '3453', '1927', '8779', '7875', 'l', 'I', '3415', '2997', 'O', '4555', '9533', 'd']