You have a right triangle and know the length of the hypotenuse and opposite leg (opposite to angle theta)
Then, you use the trigonometric function of sine of the angle as follow:
[tex]\begin{gathered} \sin i\theta=\frac{oppoite}{hypotenuse} \\ \\ \sin \theta=\frac{8in}{16in} \\ \\ \theta=\sin ^{-1}(\frac{8}{16}) \\ \\ \theta=30 \end{gathered}[/tex]
