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.
['3743', '7301', 'F', 'c', '8983', '8179', 'P', '1829', '8565', 'L', 'L', 'P', 'K', 'T', '7949', 'X', 'J', '6903', '2283', '5967']