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', '447', '9781', 'R', '6083', 'u', '9229', 'Z', 'F', '2437', '9677', 'n', 'G', '6763', '5883', 'B', '9563', '4575']