Use the Cars data to conduct a stepwise regression analysis.
a. Calculate seven regression models, each with one of the following explanatory variables: Cy1, Liter, Doors, Cruise, Sound, Leather, and Mileage. Identify the explanatory variable that corresponds to the model with the largest R2 value. Call this variable X1.
b. Calculate six regression models. Each model should have two explanatory variables, X1 and one of the other six explanatory variables. Find the two-variable model that has the highest R2 value. How much did R2 improve when this second variable was included?
c. Instead of continuing this process to identify more variables, use the software instructions provided to conduct a stepwise regression analysis. List each of the explanatory variables in the model suggested by the stepwise regression procedure.