For ideal gases at constant volume, you can use the law of Gay - Lussac:
P / T = constant => P1 / T1 = P2 / T2
=> P2 = T2 * P1 / T1
And remember you have to use absolute scale of temperature.
T1 = 25 + 273.15 = 298.15 K
T2 = 475 + 273.15 = 748.15 K
=> P2 = 748.15 K * 1.8 atm / 298.15 K = 4.5 atm
Answer: 4.5 atm