Two loudspeakers emit sound waves of the same frequency  along the x-axis. The amplitude of each wave is a. The sound  intensity is minimum when speaker 2 is 10 cm behind speaker 1.  The intensity increases as speaker 2 is moved forward and first  reaches maximum, with amplitude 2a, when it is 30 cm in front  of speaker 1. What is

a. The wavelength of the sound?

b. The phase difference between the two loudspeakers?

c. The amplitude of the sound (as a multiple of a) if the speakers  are placed side by side?