4.2-9 The system shown in Fig. P4.2-9 is used for scrambling audio signals. The output y(t) is the scrambled version of the input m(t). (a) Find the spectrum of the scrambled signal y(t). (b) Suggest a method of descrambling y(1) to obtain m(t). Figure P.4.2-9 M(f) Low-pass filtr 0-15 kHz m(1) y(1) (Scrambled output) 15 kHz f kHz - 15 kHz 2 cos 30,000nt