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.
['X', '7281', 'R', '8635', '3765', 'Y', '9213', '4011', 'F', 'D', 'E', '2327', 'F', '5441', '5797', '1503', 'r', '2841', '6863']