The figure shows two loudspeakers $($A$)$ and $($B$),$ and a point $($C$)$ where a listener is positioned. The speakers vibrate in phase and are playing a $61\mathrm{.}0$ Hz tone. The speed of sound is $336\frac{m}{s}.$ The listener at point $($C$)$ hears the second destructive interference at a distance $4\mathrm{.}00$ m as measured from speaker $($A$).$ What is the separation $($d$)$ between the two speakers?