In Problem 13.5 on page 470, you used the percentage of alcohol and chlorides to predict wine quality (stored in VinhoVerde). Using the results from that problem,

a. Construct a 95% confidence interval estimate of the population slope between wine quality and the percentage of alcohol.

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.