Thermal Equilibrium: Calculating Pressure of Helium Gas in 3.11L Container

[Indy2424]

Homework Statement

A sealed, evacuated 3.11 liter container initially contains 0.87 liter of liquid helium. As the contents of the container come into thermal equilibrium with the surroundings, the liquid helium vaporizes and turns into gas. If the temperature of the laboratory is 24.8°C, what is the pressure of the helium gas inside the container? (Note: The density of liquid helium is 122.1 kg/m3.)

Homework Equations

Truthfully I don't have any idea on how to set this up. Any help at all would be thankful.
Thanks

The Attempt at a Solution

 

[LowlyPion]

Figure first the mass of the helium in the container.

The total mass divided by the atomic mass will tell you how many moles of helium atoms you have inside.

At that point it's

PV = nRT isn't it?
http://en.wikipedia.org/wiki/Ideal_gas_law

You know T, you know V and you know n moles so ...

 

[Indy2424]

Yep that was it all along i was just missing a step and using the wrong constant. Thanks