Calculating Distance of Two Speakers Producing 162Hz Sound

[lilkrazyrae]

Two speakers produce a 162Hz sound in phase. If an intensity minimum is located 3.75m from the nearer speaker, find the distance to the further speaker if the speed of sound in the air is 345m/s.

Would it go like this
d(1)-d(2)/wavelength=phase difference/2pi
x-3.75/2.13=1/2pi
x=4.09m

This doesn't seem quite right let me know what to do please.

 

[Andrew Mason]

Two speakers produce a 162Hz sound in phase. If an intensity minimum is located 3.75m from the nearer speaker, find the distance to the further speaker if the speed of sound in the air is 345m/s.
Would it go like this
d(1)-d(2)/wavelength=phase difference/2pi
x-3.75/2.13=1/2pi
x=4.09m
This doesn't seem quite right let me know what to do please.

The difference in distance must equal a multiple of half a wavelength for a minimum (phase difference = $n\pi$ not $2n\pi$).

AM