Two In-Phase Loudspeakers That Emit Sound with the Same Frequency

Multiple Choice

Two in-phase loudspeakers that emit sound with the same frequency are placed along a wall and are separated by a distance of 8.00 m. A person is standing 12.0 m away from the wall, equidistant
From the loudspeakers. When the person moves 3.00 m parallel to the wall, she experiences
Destructive interference for the second time. What is the frequency of the sound? The speed of
Sound in air is 343 m/s.

A) 694 Hz
B) 562 Hz
C) 422 Hz
D) 452 Hz
E) 278 Hz