A right cylinder with a radius of 2 feet and height of 6 is filled with water. When laying the cylinder horizontally (so gravity is forcing the water on the sides), the water is 3 feet deep. How deep is the water if the cylinder is laid vertically?

Knowing this, I thought that because the diameter is 4, and the water is 3, the volume of the water should be 3/4 that of the cylinder. I eventually got the answer of 4.5 feet, and so did everyone else, but the teacher said that's wrong. So what's the answer and how do you find it? I can't find any other way . . . thanks!

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