Two identical loudspeakers are placed on a wall 3.00 m apart. A listener stands 5.00 m from the wall directly in front of one of the speakers. A single oscillator is driving the speakers at a frequency of 300 Hz. (a) What is the phase difference in radians between the waves from the speakers when they reach the observer? (Your answer should be between 0 and 2π.) rad (b) What is the frequency closest to 300 Hz to which the oscillator may be adjusted such that the observer hears minimal sound? Hz