Using the yearly amount of solar power generated by utilities (in millions of kWh) in the United States from 2002 through 2016 data for Problem 16.16 on page 645 (stored in SolarPower),

a. Fit a third-order autoregressive model to the amount of solar power installed 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 amount of solar power installed 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 amount of solar power installed and test for the significance of the first-order autoregressive parameter. (Use α = 0.05.)

d. Forecast the yearly amount of solar power generated by utilities (in millions of kWh) in the United States in 2017 and 2018.