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', '8735', '3445', 'T', 't', '4799', '9365', '3943', 'C', '1599', '8421', '1193', 'L', 'A', '5507', '9517', '5645', 'b']