1. Answer the following questions about a theoretical time series y. (30 points) (a) Write out the formula for an ARIMA(4,2,0) model. (5 points) (b) What would you expect that ACF and PACF plots to look like for this Time Series? Explain why this is the case. (10 points) ((3) Write out the formula for an ARIMA(3,2,1) model. (5 points) ((1) How can you determine Whether the model in part (a) ts the data better than the model in part (c)? Explain in detail. (10 points)