Two Loudspeakers Are Placed Side by Side and Driven by the Same

Two loudspeakers are placed side by side and driven by the same source at 490 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.If one of the speakers is gradually pushed toward the listener,how far must it be moved to repeat the condition of constructive interference at the listener's ear? (The speed of sound = 340 m/s. )

A) 1.44 m
B) 0.69 m
C) 0.35 m
D) 0.17 m
E) ​2.88 m