Okay, so this is a PV=NRT problem
We know that V1/T1 = V2/T2 from the formula.
T1 is given as 25 degrees
V1 is given as 5 Liters
If the temperature decreases by 10 degrees, then T2 would be 25-10, so V2 is 15
Now, we can plug everything into the formula
5/25 = T2/15
(5/25) * 15 = T2
Therefore, T2 = 5/25 * 15L. When you simplify this, you get 3L
Therefore, the new volume of the gas is 3L
Hope this helped ^_^