Answer:
666.7 Hz
Step-by-step explanation:
Light is an example of electromagnetic wave. Electromagnetic waves consist of oscillations of electric and magnetic fields that propagate through space. They are transverse waves, and they all travel through a vacuum at a speed of

called speed of light.
The relationship between frequency and wavelenght for an electromagnetic wave is given by the equation:

where
f is the frequency of the wave
is its wavelength
In this problem, the light wave has a wavelength of

Therefore, by using the equation above, we can find its frequency:
