(a) Determine the critical values for a right-tailed test of a standard population deviation with 18 degrees of freedom at \(\alpha=0.1\) level of significance.

(b) Determine the critical values for a left-tailed test of a standard population deviation for a sample size of \(n=30\) at \(\alpha=0.05\) level of significance.

(c) Determine the critical values for a two-tailed test of a standard population deviation for a sample of size \(n=23\) at \(\alpha=0.05\) level of significance.