$$\lambda=\frac{c}{f}$$

Where \(c\) is the wave's speed and \(f\) is its frequency.

For electromagnetic waves in a vacuum (like light) \(c\) is the speed of light, \(2.998\times10^8 \text{ m/s}\). But for sound waves in air at \(20\degree\text{C}\), the speed is \(343 \text{ m/s}\).

Substituting in the given frequency \(f=268 \text{ Hz}\) we obtain:

$$\lambda=\frac{343\text{ m/s}}{268 \text{ Hz}}=1.28 \text{ m}$$

To convert to feet we multiply by the conversion factor \((3.28\text{ ft})/(1\text{ m})\):

$$1.28\text{ m}\left(\frac{3.28\text{ ft}}{1\text{ m}}\right)=\boxed{4.21 \text{ ft}}$$