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', 'b', 'G', 'H', '255', '6809', '5133', '1059', '4317', 'P', '7219', 'd', '805', 'G', '5243', '8305', '8509', 'o']