Answer
Please see the work below.
Work Step by Step
We know that
$t=\sqrt{\frac{2h}{g}}$
The horizontal distance covered by the projectile is given as
$x=v_{\circ}t$
$\implies x=v_{\circ}\sqrt{\frac{2h}{g}}$
$x=\sqrt{\frac{2v_{\circ}^2 h}{g}}$