In this question, we have a gas going through a change in temperature and the law that shows the relationship between temperature and volume is Charles's gas Law, which can be presented with the following formula:
V1/T1 = V2/T2
We have:
V1 = 40 L
T1 = 300 K
V2 = ?
T2 = 50 K
Now we just need to add these values into the formula:
40/300 = V2/50
0.1333 = V2/50
V2 = 6.7 Liters will be the new volume
