圆 A 的半径是圆 B 半径的 3 倍。 圆 A 从 X 滚动到 Y 需要转动 12 圈。（取 $\pi = 3.14$）

1. Relate the circumferences of Circle A and Circle B

Since the radius of Circle A is $3$ times the radius of Circle B, the circumference of Circle A is also $3$ times the circumference of Circle B.

2. Calculate the number of revolutions for Circle B

The distance from X to Y is constant. Since Circle B has $\frac{1}{3}$ the circumference of Circle A, it needs $3$ times as many revolutions to cover the same distance.
Number of revolutions $= 12 \times 3 = 36$

1. Calculate the circumference of Circle A

$\text{Circumference} = 2 \times \pi \times r = 2 \times 3.14 \times 12 = 75.36 \text{ cm}$

2. Calculate the total distance XY

$\text{Length of XY} = 12 \times 75.36 = 904.32 \text{ cm}$