A circular cardboard with a diameter of 15 decimeters rolls once on the meter stick, how many decimeters will it pass?
一个圆形硬纸板的直径为15分米，在米尺上滚动一周，通过的距离是多少分米．
<gadget id="calculator">3.14 * 15</gadget>
<output>47.1</output>

<result>47.1</result>