At constant volume, a tank of gas shows a pressure of 2500 atm at 290 k. the tank is then placed in a metal shed where the temperature is 320 k. what is the new pressure?

Gay-Lussac's law states the relationship between pressure of gas with temperature. It states that pressure of gas is directly proportional to temperature of gas at constant volume.
P/T = k
where P - pressure, T-temperature and k-constant 
P1/T1 = P2/T2
where parameters for the 1st instance are on the left side and parameters for the 2nd instance are on the right side.
2500 atm/ 290 K = P/320 K 
P = 2759 atm 

3cmx4cm =12cm / 2= 6cm