Grandpa is getting old, and his eyes are a bit blurry. He can see objects about 30 centimeters most clearly. How far away should the mirror be placed from your face when grandpa shaves?
爷爷年纪大了，眼睛有些花，他对30厘米左右的物体看得最清楚，你说爷爷每欠刮胡子应该把镜子放在距离自己脸多远处最合适？
<gadget id="calculator">30 / 2</gadget>
<output>15</output>

<result>15</result>