a. Plot the series. What can you learn from examining this plot? b. Calculate and display the first 24 autocorrelations for the series. What do the ACF and PACF suggest about the series? c. Suggest and estimate an optimal set of differencing to use with the series. d. Estimate the ARIMA model that you believe to be a good candidate for forecasting container shipments. It may help to specify the seasonality as "12." Test the Ljung- Box statistic and report your findings. Finally, plot the first 24 autocorrelations of the residuals to your best model