Mr. Liu goes to work at 8:00 am and ends at 8:00 pm every day. How many hours does he work every day?
刘老师每天上午8点上班，晚上8点下班，他每天的工作时间是多少个小时．
<gadget id="calculator">12 - 8</gadget>
<output>4</output>

<gadget id="calculator">8 + 4</gadget>
<output>12</output>

<result>12</result>