Use the model you selected in Exercise 13.77 to answer the following questions.
a. Do any of the data points appear to have high influence? Leverage? Justify your answer.
b. If you identified any high leverage or high influence points in part (a), compare the estimated models with and without these points.
c. What is your final model describing sulfur dioxide air pollution?
d. Display any other explanatory variables that may improve the fit of your model.