Xiaohua goes to bed at 9:00 in the evening. Get up at 6:00 the next morning, how many hours does he sleep.
小华同学晚上9：00睡觉．第二天早上6：00起床，他的睡觉时间是多少小时．
<gadget id="calculator">24 - 21</gadget>
<output>3</output>

<gadget id="calculator">3 + 6</gadget>
<output>9</output>

<result>9</result>