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.
['S', '8769', 'y', '1009', 's', '6083', 'I', 'g', 'm', '4703', 'w', 'T', 'O', 'X', '6927', '8259', '9125', '8309', '4661']