A linear time-invariant system is described by the difference equation y[n] = x[n] + x[n-4] (a) Find its impulse response h[n]. (b) Find its system function H (2). (c) Plot the poles and zeros of H (2) in the z-plane. (Recall that -1=ejk where k is an odd integer.) (d) Find the frequency response H(e) and express it in polar form (magnitude and phase). (e) Carefully sketch and label a plot of IH(e) for-