$6\mathrm{.}2-2$

$($a$)$ The bandwidth is $15kHz.$ The Nyquist rate is $30kHz.$

$($b$)65536=2^{16}$ so that $16$ binary digits are needed to encode each sample.

$($c$)3000016=480000$ bits $\frac{?}{s}.$

$($d$)4410016=705600$ trits $\frac{?}{s}.$