Let's find the temperature when the pressure is equal to zero. There are two ways of doing this, what are they? What is the temperature when the pressure equals zero? What is the significance of that number?

The lower the temperature, the lower the pressure inside of the sphere. If the exact values were plotted out, a linear relationship would be apparent. Extrapolating this line to the point where there would be no pressure yields absolute zero, which is about -273.15 degrees Celsius.