Write a function, window_avg, that takes a list of numbers and an integer n. The function calculates and returns the cumulative average of numbers, up to position n. NOTE: Round your result to one decimal point.

Johnson enterprises uses a computer to handle its sales invoices. lately, business has been so good that it takes an extra 3 hours per night, plus every third saturday, to keep up with the volume of sales invoices. management is considering updating its computer with a faster model that would eliminate all of the overtime processing.