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.
['4939', '895', '6011', '4219', 's', 'J', 'F', 'p', 'o', '7477', 'R', '8629', '8297', '9129', 'z', '2303', 'p', '4695', '7573']