P1 / T1 = P2 / T2
In our question, we are given this information.
P1 = 1.2 atm
P2 = ?
T1 = 15 C
T2 = 30 C
Then, solve for P2.
P1 / T1 = P2 / T2
P2 = (P1 / T1) * T2
P2 = (1.2 atm / 15 C) * (30 C) = 2.4 atm
Now, the question asks the pressure change, therefore we must solve for the P2-P1
Pressure Change = P2 - P1 = 2.4 atm - 1.2 atm = 1.2 atm
This makes sense, because if the Temperature is doubled, then so is the Pressure, as long as the other parameters in the gas law are held constant.