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.
['Y', '1457', 'Y', 'L', 'l', 'm', 'O', 'h', 'H', '1319', 'R', '1325', 'l', 'G', 'I', 'c', '6873', '3031', '3791', '5085']