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.
['633', '2599', 'L', '9527', 'M', '7885', 'y', '5241', '8941', 'a', 'l', '7087', '7047', 'U', '653', 'R', '7631', '1929', '7635']