The relationship between frequency, wavelength and speed of a wave is given by:
[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 bat sound has a wavelength of
[tex]\lambda=3.7 mm=3.7 \cdot 10^{-3} m[/tex]
while the speed of the wave is just the speed of sound in air:
[tex]v=343 m/s[/tex]
Therefore, the frequency of the bat sound is
[tex]f= \frac{v}{\lambda}= \frac{343 m/s}{3.7 \cdot 10^{-3}m}=9.27 \cdot 10^4 Hz [/tex]
