Finding temperature through a manometer

[Twoism]

Homework Statement

The mercury manometer shown in the figure is attached to a gas cell. The mercury height h is 120 mm when the cell is placed in an ice-water mixture. The mercury height drops to 30 mm when the device is carried into an industrial freezer. HINT: The right tube of the manometer is much narrower than the left tube. What reasonable assumption can you make about the gas volume?
[PLAIN]http://img36.imageshack.us/img36/6331/knightfigure1650.jpg
I'm assuming the temperature is originally at 0C since it says it's in an ice-water mixture. I'm also assuming pressure is constant throughout the problem.

Homework Equations

V/T=V/T
C+273=K

The Attempt at a Solution

I attempted to do:
120/273K = 90/T
T=-68.25C
Wrong answer. I'm guessing there's more to put into the volume part of the equation than just the height, but I don't know exactly what. Can anyone help? Thanks.

 

[Twoism]

After much observation, I was wrong to conclude pressure would be the same. After reading the hint carefully, I came to the conclusion pressure changes, while volume remains constant. Still, I don't know how to find the pressure of the system.

 

[Jobrag]

p1*v1/t1=p2*v2/t2