Using Gay-Lussac's Law, we have
P2 = [tex] \frac{(T2)X(P1)}{T1} [/tex]
where, P and T stands for pressure and temperature respectively, terms 1 and 2 indicates initial and final pressure/temperature respectively.
Given that, P1 = 1.5 atm, T1 = 320 K, T2 = 450 K,
∴P2 = [tex] \frac{(450)X(1.5)}{320} [/tex] = 2.1 atm