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.
['2991', '43', 's', '8979', '6385', '8755', '2059', '1391', 'O', '7257', 'w', '5581', '5029', '9391', 'Q', 'j', 'I', 'S']