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.
['U', 'A', '4443', '5987', '9109', '8837', '3753', 'f', '1609', '4219', 'T', '6559', 'N', '4735', '7751', 'j', 'W', 'r', '6507']