The water should fill the aquarium to 1.5 feet
Solution:
Given that the directions for the aquarium say that it should be filled with 9 cubic feet of water.
This means volume of aquarium is 9 cubic feet
Given that aquarium is 2 feet wide and 3 feet long
To find: Height of aquarium
Since a aquarium is in shape of cuboid, we can use the volume of cuboid formula
The volume of cuboid is given as:
volume of cuboid =

Where "l" is the length
w is the width
"h" is the height
Substituting the values, we get,

Thus the height of aquarium is 1.5 feet