4. The sales (in millions of dollars) for a 15-month period are as follows. Month 1 2 3 Sales 390 565 395 450 490 560 420 565 Month 9 10 11 12 13 14 15 Sales 470 1000 490 485 525 550 530 4 5 6 7 8 8 a. Compare a three-month moving average forecast with an exponential smoothing forecast. Use a = 0.2. Find MSE for both methods. b. Which provides the better forecasts based on MSE? c. Find the forecast for the next month using the best forecast method