(a) Compute four-week and five-week moving averages for the time series. (b) Compute the MSE for the four-week and five-week moving average forecasts. (c) What appears to be the best number of weeks of past data (three, four, or five) to use in the moving average computation? Recall that the MSE for the three-week moving average is 10.22. Use the best method (among three-, four-, and five-week MA) to forecast sales for week 13.