Xiao Ming went to bed at 21:00, and got up at 7:00 the next morning. How many hours did Xiao Ming sleep?
小明21时睡觉，第二天早上7时起床，小明睡了多少小时．
<gadget id="calculator">3 + 7</gadget>
<output>10</output>

<result>10</result>