The frequency of the wave is 4.68 kHz
.
The formula connecting frequency f and wavelength λ is
fλ = c,
where c = the speed of light [2.998 × 10^8 m·s^(-1)]
We can rearrange the formula to get
f = c/λ
∴ f = 2.998 × 10^8 m·s^(-1)/6.40 × 10^4 m= 4.68 × 10^3 s^(-1) = 4.68 × 10^3 Hz
= 4.68 kHz
