Answer:
6 liters.
Explanation:
So we have a glass, a jar, and a pitcher and together, they hold 54 liters.
We are told that the jar has the same volume as 3 glasses and the pitcher has the same volume as 5 glasses. In other words, let g denote glasses, j denote jars, and p denote pitchers:

Since jar is the same as 3 glasses, this means that j=3g. And since the pitcher is the same as 5 glasses, this means that p=5g. Substitute:

Combine like terms:

Divide both sides by 9. The left cancels:

Therefore, the volume of the glass is 6 liters.