The angle of projection at which the horizontal range and the maximum height of a projectile are equal is

$\text{H}=\text{R}$              {given}

$\Rightarrow$  $\frac{\cancel{u^2}{\sin }^2\theta }{2\cancel{g}}=\frac{\cancel{u^2}\sin 2\theta }{\cancel{g}}$

$\Rightarrow$  ${\sin }^{\cancel{2}}\theta =2\left(2\cancel{\sin \theta }\cos \theta \right)$         $\left\{\sin \theta \ne 0\right\}$

$\Rightarrow$  $\sin \theta =4\cos \theta$

$\Rightarrow$  $\tan \theta =4$

$\Rightarrow$  $\because \theta ={\tan }^{-1}4={75.96}^0\approx {76}^0$