Answer
See below.
Work Step by Step
$z=\frac{\overline{x}-\mu}{\sigma/\sqrt n}=\frac{87.6-100}{15/\sqrt{113}}\approx-8.79$
Thus, using the table, the probability of obtaining a result more extreme than $z$: $P(Z\lt-8.79)\approx0$.
If $P\lt\alpha$, then the null hypothesis is rejected. $0\lt0.05$, thus we reject the null hypothesis. Thus there is sufficient evidence to support the claim that the mean IQ for the very-low-birth-weight population is less than $100$.
