Two in-phase loudspeakers that emit sound with the same frequency are placed along a wall and are separated by a distance of 2.4 m. a person is standing 10.0 m away from the wall, equidistant from the loudspeakers. when the person moves 0.20 m parallel to the wall, she experiences destructive interference for the first time. what is the frequency of the sound? take the speed of sound in air to be 343 m/s.