Answer
See below.
Work Step by Step
The sample mean is: $\overline{x}=\mu\pm z\frac{\sigma}{\sqrt n}$, which here is: $8\pm1.96\frac{2}{\sqrt{5}}\approx0.5202$. Hence the null hypothesis is rejected if $\overline{x}\geq9.7531$ or $\overline{x}\leq6.2469$