Retail sales in Quarters 1–4 over a 10-year period for a department store are shown (in hundreds of thousands of dollars) in the table below. Year Quarter 1 2 3 4 1 8.3 10.3 8.7 13.5 2 9.8 12.1 10.1 15.4 3 12.1 14.5 12.7 17.1 4 13.7 16.0 14.2 19.2 5 17.4 19.7 18.0 23.1 6 18.2 20.5 18.6 24.0 7 20.0 22.2 20.5 25.1 8 22.3 25.1 22.9 27.7 9 24.7 26.9 25.1 29.8 10 25.8 28.726.032.2

a. Write a regression model that contains trend and seasonal components to describe the sales data.

b. Use least squares regression to fit the model. Evaluate the fit of the model.

c. Use the regression model to forecast the quarterly sales during year 11. Give 95% prediction intervals for the forecasts.