What is the frequency of light with a wavelength of 7.245×10−7 m in glass?

[elitepro]

Homework Statement

The glass prism has an index of refraction
that depends on the wavelength of the light
that enters it. The index of refraction is
1.44 for light of wavelength 7.245 × 10−7 m
in a vacuum and 1.79 for light of wavelength
4.433 × 10−7 m in vacuum. A beam of white
light is incident from the left, perpendicular
to the first surface, as shown in the figure,
and is dispersed by the prism into its spectral
components.

Determine the frequency of the 7.245×10−7 m
light in the glass.
Answer in units of Hz

Homework Equations

c = λf

The Attempt at a Solution

Alright so I calculated the frequency to be 5.03125e-7 (this is correct),
so I just plugged this into the formula 3*10^8/5.03125e-7 and got 5.96*10^14 m
I thought I did this correctly. Did I do something silly?

 

[haruspex]

Alright so I calculated the frequency to be 5.03125e-7 (this is correct),

I don't see how it can be. How do you know it is right? Please post your calculation.