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.
['1535', '7791', '6341', '2679', '4953', '3305', '1549', 'L', 'K', 'D', 'l', 'y', 'i', 'u', '4495', 'S', '3661', 'e']