Answer:
a) 
b) As t increases from 3 to 6, v varies from 18 gallons to 12 gallons.
Step-by-step explanation:
The volume of the tank in terms of the time can be described by the following equation:

In which V(0) is the initial volume and a is the hourly decrease rate.
a. Write a formula that expresses v in terms of t.
The tank initially contains 24 gallons of water, which means that 
Drains at a constant rate of 2 gallons per hour, so 
Then


b. As t increases from 3 to 6, v varies from _________ to _________



So as t increases from 3 to 6, v varies from 18 gallons to 12 gallons.