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.
['4177', 'd', 'b', 'm', 'f', 'R', '797', '7905', '4355', '7515', '9801', 'F', 'R', '9125', '8445', 'k', 'K', 'K']