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', '373', '6865', 'v', 'u', '1811', '3893', 'Z', '6001', '9787', 'c', 'K', 'P', '9065', 's', 's', 'M', '6833']