Answer
$46.2^{\circ}$
Work Step by Step
At the highest point, we know that the final velocity becomes zero:
$\implies v_y=0$
$v_{\circ}sin\theta -gt=0$
This simplifies to:
$\theta=sin^{-1}(\frac{gt}{v_{\circ}})$
We plug in the known values to obtain:
$\theta=sin^{-1}(\frac{9.81(0.750)}{10.2})$
$\theta=46.2^{\circ}$
