In this question, we have a situation where all 3 known gas laws are being used in what is called the Combined gas law, and the formula for this law is:
P1V1/T1 = P2V2/T2
We have:
P1 = 100 kPa, or 0.987 atm
V1 = 2.50 Lites
T1 = 303 K
P2 = 90 kPa, or 0.888 atm
V2 = 3.75 L
T2 = ?
Now we add these values into the formula:
0.987 * 2.50/303 = 0.888 * 3.75/T2
2.47/303 = 3.33/T2
0.00815 = 3.33/T2
T2 = 408 K is the new temperature