A sinusoidal signal of frequency A?0 = 104/2π Hz is sampled

A sinusoidal signal of frequency A?0 = 104/2p Hz is sampled at the rate of 8 kHz and then applied to a sample-and-hold circuit to produce a flat-topped PAM signal s (t) with pulse duration T = 500Âľs
(a) Compute the waveform of the PAM signal s (t).
(b) Compute | S (A?) |, denoting the magnitude spectrum of the PAM signal s (t).
(c) Compute the envelope of | S (A?) |. Hence confirm that the frequency at which this envelope goes through zero for the first time is equal to (1/T) = 20 kHz.