4. Consider the two series Xt = Wt Yt = Wt - OWt-1 + Ut, where We and Ut are independent white noise series with variances on and on, respectively, and 0 is an unspecified constant. 4.1 Show that Yt is stationary. Express the ACF, py(h), for h = 0, +1, 12, ... of the series Yt as a function of ow, oh, and 0. 4.2 Show that Xt and Yt are jointly stationary. Determine the CCF, Pry (h) relating Xt and Yt