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.
['7455', 'd', '93', '9467', '7391', '1693', '525', '9121', '4913', 'z', '4615', 'C', '4809', '927', '623', '3417', '323', 'W', '6809', '15']