For the regression equation obtained in Exercise 15.57, analyze the residuals by
(a) Constructing a histogram,
(b) Using a normal probability plot,
(c) Plotting the residuals versus the x values, and
(d) Plotting the residuals versus the order in which they were observed. Do any of the assumptions of the simple linear regression model appear to have been violated? Comment on whether any of the years were associated with especially high or low fuel consumption for the number of flying hours during the year.