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.
['7997', '6973', '5735', '6487', 'Z', '9771', 'M', '1269', 'r', '6473', '7983', 'B', 'A', 'B', '3233', 'Q', 'Y', 'R', '6885']