Xiaoli goes to bed at 21 o'clock every day and gets up at 6 o'clock in the morning. How many hours does she sleep every day?
小丽每天21时上床睡觉，早上6时起床，她每天睡了多少小时．
<gadget id="calculator">3 + 6</gadget>
<output>9</output>

<result>9</result>