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.
['6531', 'w', '8817', '3845', 'N', '3827', '7153', '4943', '9651', '5323', 'x', '5553', '949', '4203', 'z', '549', '3817', '3515', 'M']