The basic relationship between frequency, wavelength and speed of a wave is given by
[tex]v=\lambda f[/tex]
where
v is the wave speed
f is its frequency
[tex]\lambda[/tex] is its wavelength
Re-arranging the equation and using the data of the problem, we find the frequency of the wave:
[tex]f= \frac{v}{\lambda}= \frac{65 m/s}{0.8 m}=81.3 Hz [/tex]
