Answer
$$ \theta=\sin^{-1}\left(\frac{814}{3000}\right)\approx 15.74^{\circ}$$
Work Step by Step
Since
$$ h=-16t^2+vt \sin\theta $$
at $ v=1500, \ \ h= 750,\ \ t=2$, then
\begin{aligned}
h&=-16t^2+vt \sin\theta \\
750&=-16(4)+3000 \sin\theta \\
814&= 3000 \sin\theta\\
\sin\theta &=\frac{814}{3000}
\end{aligned}
hence $ \theta=\sin^{-1}\left(\frac{814}{3000}\right)\approx 15.74^{\circ}$
