Xiao Ming goes to school at 7:00 in the morning and comes home from school at 4:00 in the afternoon. How many hours does he spend at school?
小明早上7：00到学校上课，下午4：00放学回家，他在学校的时间是多少小时．
<gadget id="calculator">4 + 12</gadget>
<output>16</output>

<gadget id="calculator">16 - 7</gadget>
<output>9</output>

<result>9</result>