Wavelength, Frequency, & Speed of Light in Different Media

[jcvince17]

Homework Statement

A beam of light from a monochromatic laser shines into a piece of glass. The glass has thickness L and index of refraction n=1.5. The wavelength of the laser light in vacuum is L/10 and its frequency is f. In this problem, neither the constant c nor its numerical value should appear in any of your answers

How long does it take for a short pulse of light to travel from one end of the glass to the other?
Express your answer in terms of some or all of the variables f and L. Use the numeric value given for in the introduction.

Homework Equations

c = $$\lambda$$ * f
f = 1/t
n = c/v

The Attempt at a Solution

t = 15/f

i know this answer is correct, but I still cannot come up with how the correct answer was derived.
https://www.physicsforums.com/archive/index.php/t-225369.html

 

[mgb_phys]

The speed in the glass is c/n = c/1.5
The time through the glass is distance/speed = L / (c/1.5)
Since you know c = $$\lambda$$ * f, you simple have to rearrange the equation subsituting for c.

 

[jcvince17]

thanks you. i will begin working out the substitution.