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.
['z', 'j', 'Z', '8161', '6927', 'w', '3803', '1205', '6633', '9921', 'u', 'a', 'u', '5683', '8421', '4643', 'B', '6155', '9671']