Relating resonance with two different Pipes

[RoxSox2004]

Homework Statement

A pipe, open at one end, has a leng
produces pipe A, open at one end, and pipe B, o

A pipe, open at one end, has a length L. Cutting this pipe crosswise
produces pipe A, open at one end, and pipe B, open at both ends.
a. For what length of pipe A will the third lowest resonant frequency of pipe A be equal
to the lowest resonant frequency of pipe B?

Homework Equations

v = (lambda)(f)

5th harmonic of A, f = (5v)/(4L)
1st Harmonic of B, f = v/2L

The Attempt at a Solution

I've been fairly stumped by this one. I don't get exactly how to set it up. I tried setting the frequencies equal to each other, but it doesn't work.

 

[RoxSox2004]

I'm really just looking for a hint to set me on the right path.