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.
['d', 'c', '7251', '2923', '6115', 'n', '4673', 'm', '8145', '4637', 'G', 'k', 't', 'l', 'Q', '9305', '6053', '3595', 'o']