The ideal gas law is:

PV = nRT

where P = pressure of the gas, V = volume of the gas, T = the temperature of the gas, and you can consider n and R as constants.

For a container of constant volume, you vary the pressure and measure the resultant temperature. You then plot temperature vs pressure (with temperature on the vertical axis and pressure on the horizontal axis). From the ideal gas law, you would expect a straight line. What would you expect to be the gradient of that straight line?