3.14. Determine which of the following linear systems is causal. b. y(n) = x(n+4)+0.5x(n) - 2x(n-2) 3.18. Find the unit-impulse response for each of the following linear systems. b. y(n) = 0.5y(n - 1) + 0.5x(n); for n ≥ 0, y(-1) = 0