An aquarium has a length of 20 inches, a width of 10 inches, and a height of 18 inches. the directions tell you to fill the aquarium until you have a 2-inch gap between the top of the water level and the top of the aquarium. what is the volume of the water?
400 in.3
3,600 in.3
3,200 in.3
2,304 in.3

The answer is 3,200 in.3

The volume of the rectangle (V) with length l, width w, and height h is:
V = l * w * h

If you want to fill the aquarium until you have a 2-inch gap between the top of the water level and the top of the aquarium, then the height of the water space is 2 inches smaller than the height of the aquarium. Therefore:
l = 20 in
w = 10 in
h = 18 in - 2 in = 16 in

The volume of the water is:
V = 20 * 10 * 16 = 3,200 in³