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', 'g', 'F', 'K', '8221', '7385', '8791', 'A', 'w', '6391', '77', 'W', 't', '4979', '2779', 'm', '9399', '9009', 'b']