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
