3/4 of half a gallon of water

Since 12 gallons of water fill the tank to 3/4 capacity, we know that 12 gallons is 3/4 of the total capacity. Hence,
.
The last equation tells us that .
B.
We will say that D is the number of half-gallon bottles that can be filled with the water of the tanke, note that D times 1/2 must be the total capacity of the tank. Hence,

and so, we get that