The wavelength of a sound wave is related to its frequency by the relationship:
[tex]f= \frac{v}{\lambda} [/tex]
where
f is the frequency
v is the speed of the wave
[tex]\lambda[/tex] is the wavelength
The wave in our problem has wavelength of [tex]\lambda=20.0 m[/tex] and speed of [tex]v=343 m/s[/tex] (this is the speed of sound in air), therefore its frequency is
[tex]f= \frac{343 m/s}{20.0 m}=17.15 Hz [/tex]
And the period of the wave is equal to the reciprocal of its frequency:
[tex]T= \frac{1}{f}= \frac{1}{17.15 Hz}=0.058 s [/tex]
