A doorman goes to work at 9 o'clock in the evening and leaves at 7 o'clock the next morning, how many hours does he work?
一个门卫晚上9时上班，第二天早上7时下班，他工作的时间是多少小时．
<gadget id="calculator">12 - 9</gadget>
<output>3</output>

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

<result>10</result>