$8\mathrm{.}3-3$ A compact disc $($CD$)$ records audio signals digitally by means of a binary code. Assume an audio signal bandwidth of $15$ kHz$.($a$)$ What is the Nyquist rate? $($b$)$ If the Nyquist samples are quantized into $65,536$ levels $($L $=65,536)$ and then binary$-$coded, what number of binary digits is required to encode a sample?