4. (a) Write a computer program to simulate the discrete-time system shown below and plot its output. Make your program correspond to the given simulation diagram; that is, program coupled difference equations in variables that correspond to the outputs of the delay blocks. (b) Run your program to obtain the sequence y(k), assuming x(k) is the unit step sequence and given zero initial conditions in all delay blocks. 0.6 x(k) y(k) 0.8 0.4