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.
['n', '2427', '6259', 'f', '4797', '8657', 'M', 's', '3229', '8201', 'p', 'g', 'C', 'g', '5435', 'x', '1061', '8419', '4107', 'k']