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.
['w', '107', '6471', '51', '5701', '5005', 'S', 'V', '3485', '3855', 'z', 'Q', '8123', 'i', 'v', '8447', '9153', '4639']