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.
['R', '5379', '5571', 'h', '1881', '7879', '7117', 'Z', '8427', 'R', 'J', 'H', 'h', '5153', 's', 'Q', 'F', '2977', '4039']