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.
['6509', '4845', 'r', '2053', '7293', '7793', 'M', 'j', 'Z', '555', 'e', 'k', '5149', 'M', '5101', 'N', '6999', 'B', 'L']