We will determine the angle as follows:
[tex]\sin (\theta)=\frac{10}{\sqrt[]{10^2+30^2}}\Rightarrow\sin (\theta)=\frac{10}{10\sqrt[]{10}}\Rightarrow\sin (\theta)=\frac{1}{\sqrt[]{10}}[/tex][tex]\Rightarrow\theta=\sin ^{-1}(\frac{1}{\sqrt[]{10}})\Rightarrow\theta=18.43394882[/tex][tex]\Rightarrow\theta\approx18.5[/tex]So, he must shot at an angle of approximately 18.5°.
