That sounds about right Steff. Now let's move to part c:
(c) Compute the expected value E[x(t − k)e(t − k)], for k = 0, 1, 2, . . ..
x(t) = ((A(q) − B(q))/B(q)) v(t)
where
v(t) = (B(q)/A(q) )e(t)
substituting v(t) into x(t) we get
x(t) = ((A(q) − B(q))/B(q))*(B(q)/A(q) )e(t) --->...