8. Suppose that you work for a U.S. senator who is contemplating writing a bill that would put a national sales tax in place. Because the tax would be levied on the sales revenue of retail stores, the senator has asked you to prepare a forecast of retail store sales for year 8 , based on data from year 1 through year 7 . The data are: Assignment a: Exercise 8 (page 45). Use the Retail Stores Sales data for years 1 through 7. Use the Nave Forecasting Model presented in the chapter to prepare a forecast of retail stores sales for each of the years 2 through 8 . (10 points) Assignment b: Use the above data for Assignment 1b and prepare a time-series graph of the actual and forecast values of retail store sales for the entire period and plot two graphs on the same chart, using Excel (note: you will not have a forecast for period 1 nor an actual for period 8 ). (10 points) Assignment c: Calculate the MAPE for your forecast series using the values for year 2 through year 7. (10 points)