There is a Smurf who lives in the forest. He starts from where he lives and fetches water from the river every day. He walks 5 meters per second with an empty bucket, and 3 meters per second with a full bucket of water. It takes 8 minutes to carry water back and forth. How far does the Smurf live from the river?
有一个蓝精灵住在森林里，他每天从住地出发，到河边提水回来；他提空桶每秒走5米，提满桶水每秒走3米．提一趟水，来回需要8分钟．蓝精灵的住地离河边有多远？
<gadget id="calculator">3 * 5</gadget>
<output>15</output>

<result>15</result>