Using the average baseball salary from 2000 through 2017 data for Problem 16.18 on page 645 (stored in BBSalaries),

a. Fit a third-order autoregressive model to the average baseball salary and test for the significance of the third-order autoregressive parameter. (Use α = 0.05.)

b. If necessary, fit a second-order autoregressive model to the average baseball salary and test for the significance of the second-order autoregressive parameter. (Use α = 0.05.)

c. If necessary, fit a first-order autoregressive model to the average baseball salary and test for the significance of the first order autoregressive parameter. (Use α = 0.05.)

d. Forecast the average baseball salary for 2018.