Answer:
Let V = the volume of the vessel.
Since it's given that one-third (1/3) of the volume of the vessel is filled with 5 liters of water, then we can write the following equation:
(1/3)V = 5 liters
Now, multiply both sides of the equation by 3 to find V:
3[(1/3)V] = 3(5 liters)
[3(1/3)]V = 3(5 liters)
(3/3)V = 3(5 liters)
(1)V = 15 liters
V = 15 liters is the volume of the vessel.