A random sample of $n$ measurements was selected from a population with unknown mean $\mu$ and standard deviation $\sigma$. Calculate a 90% confidence interval for $\mu$ for each of the following situations:

(a) $\ $ $n = 100, \ \overline{x} = 20.3, \ s = 4.36$
$\leq \mu \leq$

(b) $\ $ $n = 120, \ \overline{x} = 56.5, \ s = 2.65$
$\leq \mu \leq$

(c) $\ $ $n = 105, \ \overline{x} = 44.6, \ s = 3.76$
$\leq \mu \leq$

(d) $\ $ $n = 90, \ \overline{x} = 76.5, \ s = 4.35$
$\leq \mu \leq$