According to Charle's Law the volume of the gas at constant pressure is directly proportional to its absolute temperature. We expressed this as V = kT, where k is the proportionality constant. k actually is equal to n (no. of moles) times R (universal gas constant) divided by P (pressure). It is from Ideal gas equation, PV=nRT.
So when you decreased the volume of a sample of gas by a factor of three at constant pressure the temperature of the gas also decreases by a factor of three since volume is directly proportional to temperature at constant pressure.