Question on finding the frequency of a sound wave

[theskyisgreen]

Homework Statement

The distance between a node and the nearest antinode of a standing sound wave in air is 7.55 m. What is the frequency of this wave? (Use 343 m/s as the speed of sound in air.)

Homework Equations

velocity = wavelength * frequency

The Attempt at a Solution

I started by trying to find the wavelength which I deemed to be 7.55*2 = 15.1
I then just plugged it into the equation above, which got me to:
343 = 15.1 * frequency
I found the frequency to be 22.72 Hz, but apparently it's wrong and I don't understand why.

 

[rl.bhat]

The distance between a node and the nearest antinode of a standing sound wave is λ/4.