What is the frequency of a helium-neon laser with a wavelength of 632.8 nm? the speed of light is 3.00 * 108 m/s?

You must use the Plank's formula E=h*v where "h" is the Plank's constant (that means that it is given) and "v" is the frequency. There is one more way of getting the energy (E) and the formula is E = (h*c) / wavelength

So we get: h*v = (h*c) / wavelength

The final result must be

frequency = speed of light / wavelength