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', 'l', 't', 'O', '2277', '9127', 'q', '1151', 'y', '4615', 'k', '4725', 'A', '4561', '4277', 'b', '3293', 'v', '6191', '7791']