Solving Closed Pipe Question: Length Difference of 2 Pipes

[pebbles]

Homework Statement

Once closed organ pipe has a length of 3.2 m. Frequency of the note played by this pipe is 27 Hz. When a second pipe is played at the same time, a 1.50 Hz beat note is heard. By how much is the second pipe too long?

Homework Equations

?

The Attempt at a Solution

I'm really lost on this problem. I was thinking Lb-La=1/2 of wavelength, but I don't think that's right.

Any direction is appreciated. Thanks in advance.

 

[Kurdt]

Perhaps this page could get you started.

http://hyperphysics.phy-astr.gsu.edu/hbase/sound/beat.html