If a projectile is fired from ground level with an initial velocity of $v$ ft/sec and at an angle of $\theta$ degrees with the horizontal, the range $R$ of the projectile is
$$\begin{array}{ll}\text { given by } & \\\qquad R=\frac{v^{2}}{16} \sin \theta \cos \theta\end{array}.$$
If $v=80 \mathrm{ft} / \mathrm{sec},$ approximate the angles that result in a range of 150 feet.