Answer
$\theta=30^{\circ}$
Work Step by Step
The angle $\theta$ can be determined from the following formula
$\theta=sin^{-1}(\frac{v}{v_s})$
where $v$ is the speed of sound which is $343\frac{m}{s}$ and $v_s$ is the speed of source(bullet) which is given as $685 \frac{m}{s}$
Now put the values
$\theta=sin^{-1}(\frac{343}{685})=30^{\circ}$
Thus the angle $\theta=30^{\circ}$
