Consider aus_airpassengers provided by the package fpp3, the total number of passengers (in millions) from Australian air carriers for the period 1970-2011. a. [2 marks] Use ARIMA () to find an appropriate ARIMA model. What model was selected. Check that the residuals look like white noise. Plot forecasts for the next 10 periods. b. [2 marks] Write the model in terms of the backshift operator. c. [2 marks] Plot forecasts from an ARIMA (0,1,0) model with drift and compare these to the forecasts from part a. d. [2 marks] Plot forecasts from an ARIMA(2,1,2) model with drift and compare these to the forecasts from parts a and c. e. [2 marks] Plot forecasts from an ARIMA (0,2,1) model with a constant. What happens? Explain.