Two stereo speakers mounted 4.52 m apart on a wall emit identical in-phase sound waves. You are standing at the opposite wall of the room at a point directly between the two speakers. You walk 2.11 m parallel to the wall, to a location where you first notice that the sound intensity drops to zero.

If the wall along which you are walking is 10.7 m from the wall with the speakers, what is the wavelength of the sound waves?

a) 2.1 m

b) 2.9 m

c) 0.9 m

d) 1.7 m