Refer to Exercise 15-8 in which Paul Browning is interested in analyzing the effects of several variables on the weekly sales for his business. He has collected data for a sample of 20 weeks on the following variables:

Sales ($000)

Average weekly high temperature Advertising spending ($000)

Number of website hits Number of customer orders received The data are in a file called Browning.

a. Determine the estimated regression equation for this data set.

b. Calculate the residuals and the standardized residuals for this regression equation.

c. Produce the appropriate residual plot(s) to determine if the linear function is the appropriate regression function for this data set.

d. Use a residual plot to determine if the residuals have a constant variance.