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.
['n', '9205', 'H', '6775', '8113', '5579', '6865', 'R', 'S', '1531', 'r', '5789', '8435', 'q', 'm', '9177', '2955', 'c', '483']