How Deep Does the Penny Appear in a Layered Liquid Tank?

[Laxman2974]

Homework Statement

A 15-mm-thick layer of water (n = 1.33) floats on a 60-mm-thick layer of carbon tetrachloride (n = 1.46) in a tank. A penny lies at the bottom of the tank. At what depth below the top water surface do you perceive the penny? (Hint: Use the result and assumptions of Problem 21 and work with a ray diagram of the situation.)

How do I get started? DO I find the focal length?

 

[Kurdt]

Have you tried following the hint? Please post what you have attempted so far.