$y = x\tan \theta - \dfrac{gx^2}{2{v_o}^2 \cos^2 \theta}$

$0 = 150\tan \theta - \dfrac{32(150^2)}{2(70^2) \cos^2 \theta}$

$150 \tan \theta = \dfrac{3600}{49\cos^2 \theta}$

$\cos^2 \theta \, \tan \theta = \dfrac{3600}{7350}$

$\sin \theta \, \cos \theta = \dfrac{24}{49}$

$2\sin \theta \, \cos \theta = \dfrac{48}{49}$

$\sin 2\theta = \dfrac{48}{49}$

$2\theta = 78.4^\circ ~ \text{and} ~ 101.6^\circ$

$\theta = 39.2^\circ ~ \text{and} ~ 50.8^\circ$