On Friday night, Xiaohu went to bed at 9:00 pm. He thought that tomorrow would be a rest day and he could wake up later, so he set the alarm clock to ring at 8:00 am. If the alarm clock wakes up Xiaohu on time, how many hours does Xiaohu sleep?
星期五的晚上，小虎晚上9时上床睡觉，他想明天是休息日可以晚点起床，于是他把闹钟调在早上8时响铃．如果闹钟准时把小虎叫醒，小虎睡了几小时？
<gadget id="calculator">24 - 21</gadget>
<output>3</output>

<gadget id="calculator">3 + 8</gadget>
<output>11</output>

<result>11</result>