Wavelength and destructive interference

[boogiepicker]

Homework Statement

In the figure the two speakers are producing identical sound
waves. The solid lines represent constructive interference regions and the dashed lines represent destructive interference regions. The point labeled 1 is 662.15 m from the bottom speaker
and 742.9 m from the top speaker.

What is the wavelength of the sound waves

Homework Equations

v = f*lambda?, assuming v = 343 m/s
Pythagorean I believe has to be used but I'm not sure

The Attempt at a Solution

Attempted Pyth. to find distance between speakers, thinking this would be the PLD and then I'd be able to find the wavelength from there. This did not work.

Here's a picture:

 

[boogiepicker]

only way I could get correct image on here is via attachment