Two loudspeakers, $A$ and $B$, are driven by the same amplifier and emit sinusoidal waves in phase. Speaker $B$ is $12.0 \mathrm{~m}$ to the right of speaker $A$. The frequency of the waves emitted by each speaker is $688 \mathrm{~Hz}$. You are standing between the speakers, along the line connecting them, and are at a point of constructive interference. How far must you walk toward speaker $B$ to move to a point of destructive interference?