The following random sample was selected from a normal distribution: $$\begin{array}{llllllllll} 20& 15& 9& 11& 12& 16& 5& 5& 12& 4 \cr \end{array}$$

(a) $\ $ Construct a $90$% confidence interval for the population mean $\mu$.
$\leq \mu \leq$

(b) $\ $ Construct a $95$% confidence interval for the population mean $\mu$.
$\leq \mu \leq$