4. [16 points] The following figure shows a system with input of x(t) and output of y(t). This system is assembled from the four other LTI systems shown in this figure. a(t) h(z) h(t) h3(+) hy (t) a) Find the impulse response of this system based on hi(t), h2(t), h3(t) and h4(t). b) If hi(t) h2(t) h(t) = h4(t) = 8(1-2), what is the impulse response of the system? c) What is the step response of this system?