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.
['1709', 'S', 'w', '7725', 'Z', '7755', '8081', '897', 'N', '4449', 'F', 'F', 'M', 'y', 'B', 'h', 's', 'l', 's', '415']