Refer to the Grinfield Service Company discussed in Problem 14-69.
a. Develop the least squares regression equation for these variables. Plot the regression line on the scatter plot.
b. Develop a 95% confidence interval estimate for the increase in sales resulting from increasing the advertising budget by $50. Interpret the interval.
c. Discuss whether it is appropriate to interpret the intercept value in this model. Under what conditions is it appropriate? Discuss.
d. Develop a 90% confidence interval for the mean sales amount achieved during all weeks in which advertising is $200 for the week.