In Problem 14.6 on page 583, you used radio advertising and newspaper advertising to predict sales (stored in Advertise). Use the results from that problem.
a. Construct a 95% confidence interval estimate of the population slope between sales and radio advertising.
b. At the 0.05 level of significance, determine whether each independent variable makes a significant contribution to the regression model. On the basis of these results, indicate the independent variables to include in this model.