The merry-go-round at the fair rotates 12 times each minute, and children are 15 feet from the center of the wheel when they are in their seats. What is the linear velocity of the children in feet per hour?

Each rotation carries a child around a circle with circumference 2π(15) = 30π feet. At 12 rotations per minute, the child travels 12 × 30π = 360π feet per minute. Multiplying by 60 minutes per hour gives 21,600π feet per hour, so the correct choice is 21,600π.

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