Consider the time series xt = β1 + β2t + wt, where β1 and β2 are known constants and wt is a white noise process with variance σ^2w. (a) Determine whether xt is stationary. (b) Show that the process yt = xt − xt−1 is stationary. (c) Show that the mean of the moving average vt = (1/2q + 1) * ∑(q, j=-q) xt−j is β1 + β2t, and give a simplified expression for the autocovariance function.