Xiao Min goes to bed at 9 o'clock every night and wakes up at 6 o'clock in the morning. How many hours does she sleep?
小敏每天晚上9时睡觉，早上6时起床，她的睡眠时间是多少小时．
<gadget id="calculator">24 - 21</gadget>
<output>3</output>

<gadget id="calculator">6 - 0</gadget>
<output>6</output>

<gadget id="calculator">3 + 6</gadget>
<output>9</output>

<result>9</result>