Hypothesis Tests · Hard problem

Test $H_0$: $\mu = 100$ against $H_a$: $\mu < 100$ with $\sigma = 20$, $n = 16$, $\alpha = 0.025$ ($z^* = 1.96$). If in fact $\mu = 88$, what is the probability of a Type II error? Give your answer to the nearest hundredth.