Constructive/Destructive Sound Waves

[ultrapowerpie]

Homework Statement

Link to problem: http://img147.imageshack.us/my.php?image=soundqj3.png

Homework Equations

No idea, One of the reasons I'm asking. >.>

The Attempt at a Solution

Ok, I have no idea how to even begin this problem. I need a hint in the right direction, or just what the formula I need here. Thanks in advance.

 

[ultrapowerpie]

Never mind, I figured out what the relationship between the wavelength and the interferance.

http://physics.ucsd.edu/students/courses/winter2008/physics1c/documents/1.3Sound.notes.pdf

That site helped a lot.