Xiao Ming goes to bed at 9:00 every night and wakes up at 7:00 the next day. How many hours does he sleep?
小明每天晚上9：00睡觉，第二天7：00起床，他睡觉的时间是多少小时．
<gadget id="calculator">24 - 21</gadget>
<output>3</output>

<gadget id="calculator">7 - 0</gadget>
<output>7</output>

<gadget id="calculator">3 + 7</gadget>
<output>10</output>

<result>10</result>