t
1 = time for the sound of gun to reach the observer
$t_1 = \dfrac{1342 - x}{335}$
$t_1 = \dfrac{1342}{335} - \dfrac{x}{335}$
t2 = time for the sound of impact to reach the observer
$t_2 = \dfrac{1342}{503} + \dfrac{x}{335}$
$t_1 - \frac{1}{4} = t_2$
$\left( \dfrac{1342}{335} - \dfrac{x}{335} \right) - \dfrac{1}{4} = \dfrac{1342}{503} + \dfrac{x}{335}$
$\dfrac{2}{335}x = 1.088$
$x = 182.24 ~ \text{m from the target}$ answer