Xiaojun goes to bed at 9:00 every night and wakes up at 7:00 in the morning. How many hours does Xiaojun sleep every night?
小军每晚9：00睡，早上7：00起床，小军每晚睡多少个小时．
<gadget id="calculator">24 - 21</gadget>
<output>3</output>

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

<result>10</result>