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.
['C', 'w', 'g', '4513', '7967', '6861', '7981', '6381', '5057', 't', 'k', 'l', '3767', '7297', 'Z', '9943', 'D', 'Z']