When the volume and quantity of the gas are held constant, we can use the Gay-Lussac's Gas Law expressed as P1/T1 = P2/T2 in which if the pressure of the gas decreases, we know that the temperature decreases. We first convert the temperature to absolute temperature T1 = 70 + 273 = 343 K Rearranging the Gay-Lussac's equation to solve for the final temperature T2 = P2T1 / P1 = (720 mmHg)(343 K) / 740 mmHg = 334 K = 61ºC