Separate space inside from material outside - Paper 4

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An ideal right circular cylinder has radius r=9 cm and perpendicular height h=2 cm. Ignore material thickness and seams. Keep pi exact. Base area is pi r^2; volume is base area times h. Unrolling the curved surface gives a rectangle of width 2pi r and height h. A closed model has two ends; an open-top model has only one. Sketch and label the cylinder and the unrolled rectangle on separate paper.