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.
['x', '7663', '7645', '6283', 'K', '3347', '6893', '9355', 't', '3987', '5385', 'x', 'B', 'B', 'n', 'q', 'M', '5947', '6697']