a. Using a weight of 1/2 for the most recent observation, 1/3 for the second most recent. and 1/6 for third most recent, compute a three-week weighted moving average for the time series. Week 1234567 Sales (1000s of gallons) 17 21 19 23 18 16 20 8 18 9 22 10 20 11 15 12 22 25 25 20 20 15 Sales (1000s of gallons) 10 S 012 3 4 5 6 7 9 10 11 12 Week