A vessel if filled with an ideal gas at a temperature of 45 °C and at a pressure of 22.5 atm. Calculate
the temperature of the vessel when its pressure is 10.5 atm.

i used P1/T1 = P2/T2, and I got 148.4, the answer sheet says the answer is -124.6atm, how?

Hey, the method you used is correct, but your calculation must’ve gone wrong. You have to convert the kelvin to degree celsius
T2=T1 * P2/P1
T1=273.15+45=318.15k
On solving, T2=318.15 * 10.5/22.5=148.47 k
148.47-273.15=-124.6 degree celsius