Given:

Let the time at which the bucket is filled be x
We can write:
At time t = 0 , Volume (V) = 0
At time t = x, Volume (V) = 18
Using the slope formula:

Solving for x:

Recall that the domain of the function V is the time interval that satisfies the function.
Since the bucket becomes filled at 7.2min, the domain of the function V is:

Answer: Option A