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.
['D', '1025', '3853', '6283', 'y', '3449', '7757', '3363', '4103', 'o', 'E', '8551', '7095', 'C', 'f', 'U', '1507', 'X', 'r']