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', '1211', '2019', '1107', '7381', '2363', 'Y', 'd', 'Q', '5763', 'm', '7599', '8335', 'u', '487', '897', '4805', 'V', '4733', '7713']