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.
['K', 'D', '9175', '6701', '6547', 'T', '7815', 'n', '8953', '2051', '6675', 'V', '4871', 'X', 'l', 't', 't', '9617', '3313']