Two Loudspeakers Are Placed Next to Each Other and Driven

Multiple Choice

Two loudspeakers are placed next to each other and driven by the same source at 515 Hz.A listener is positioned in front of the two speakers and on the line separating them,thus creating a constructive interference at the listener's ear.What minimum distance would one of the speakers be moved back away from the listener to produce destructive interference at the listener's ear? (The speed of sound = 340 m/s. )

A) 1.5 m
B) 0.66 m
C) 0.33 m
D) 0.17 m
E) 3.0 m