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.
['4021', '8423', '3719', '4993', '3593', 'n', '9807', 'Y', 'M', '3117', '7901', '1839', 'P', 'q', 'x', 'R', '9449', 'V']