Uncle Li was on duty at 9:00 last night and left work at 7:00 the next morning. How many hours was he on duty?
李叔叔昨晚9时值班，第二天早上7时下班，他一共值班多少小时？
<gadget id="calculator">12 - 9</gadget>
<output>3</output>

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

<result>10</result>