For each of the following ARMA processes determine the order of the process and also whether they are causal and/or invertible. . (a) Xt - .75X1-1 + .5625X1-2 = W+ + 1.25Wt-1, W. ~ WN(0, 62) . (b) X+ = .80X1-1 - .15X1-2 + Wt -. 30W1-1, WI ~ WN(0, 62 ) . (c) X1 = Wt - 0.5 Wt-1 - 0.5 Wt-2 , where (W1 : t E Z) ~ WN(0, 62)