#### Answer

$\theta=17.65^{\circ}$

#### Work Step by Step

Let angle be $\theta$.
Horizontal velocity $=770cos\theta \,m/s$
So, $t=\frac{35000m}{770cos\theta} s=\frac{45.45}{cos\theta}s$
$S=ut+\frac{1}{2}at^{2}$
$0=770sin\theta\times t -4.9t^{2}$
$770sin\theta=4.9\times\frac{45.45}{cos\theta}$
$sin2\theta=0.578$
$2\theta=35.3^{\circ}$
$\theta=17.65^{\circ}$