11.89 In Exercise 11.45, we fit a second-order model to data relating the number Y of U.S. highway deaths per year to the number x1 of licensed vehicles on the road. In Exercise 11.88, we added a qualitative variable x2 to account for the presence or absence of the 55-mile-per-hour national speed limit. The accompanying SAS computer printout (Figure 11.86) gives the results of fitting the model to the data. Use this printout (Figure 11.65) and the printout for Exercise 11.45 to determine whether the data provide sufficient evidence to indicate that the qualitative variable (speed limit)

contributes information for the prediction of the annual number of highway deaths. Test by using

. Discuss the practical implications of your test results.