Goldfish bowl index of refraction

[tiger1]

Homework Statement

To a fish in an aquarium, the 4.30 mm-thick walls appear to be only 3.10 mm thick.
What is the index of refraction of the walls?

Homework Equations

m=-s'/s
n_1/s + n_2 / s' = (n_2-n_1)/R
m: magnification
s: object distance
s': image distance

The Attempt at a Solution

m=(3.1/4.3)=.72
m=-s'/s
n_1/s + n_2 / s' = (n_2-n_1)/R
1.33/s + n_2/s' = (n_2-1.33)/R

I'm not sure what R, s, or s' would be.
If I plug in the numbers I received from determing the magnification, I receive this:

1.33/4.33 + n_2/3.1 = (n_2 - 1/33)/R

 

[member 553083]

I'm not sure if this is the correct equation to solve for the index of refraction or if I'm missing something. Any help is appreciated.