Two loudspeakers, L1and L2, have the same frequency and
are in phase with each other.
An interference pattern is
produced

At position P, which is the same distance from both loudspeakers, there is a maximum. The next
maximum is at position R, where L R = 2.8 m and L R = 2.5 m.
The speed of sound in air is 340 m st. The frequency of the sound emitted by the loudspeakers is:
(A) 2.0 x 102 Hz
(B) 2.3 x 102 Hz
(C) 5.7x 102 Hz
(D) 1.1 x 103 Hz