3. Identify the following models as ARIMA (p,d,q) models (watch out for parameter redundancy), and determine whether they are causal and/or invertible. (30 points in total, 15 each) = a xtxt-1+w+ - 0.3wt-1. b xt = 1.3x-1 -0.3x-2+ wt - 0.3wt-1 4. (Question 3.43 in the textbook) Fit a seasonal ARIMA model of your choice to the U.S. Liver Birth Series (birth data set in "astsa" package). By following the process bellow (30 points in total): 1 (a) Plot the data, comment on any transformation needed. (b) Plot the acf plot and pacf plot of the transformed data and decide the appropriate model to fit. (c) Plot the diagonotic plots for the residuals and comments. (d) Repeate (b)-(c) if you think better model should be used.