A train departs at 10 o'clock in the evening and arrives at 9 o'clock in the morning the next day. How many hours does the train run in total?
一列火车晚上10时出发，第二天早上9时到达，这列火车共运行了多少小时．
<gadget id="calculator">12 - 10</gadget>
<output>2</output>

<gadget id="calculator">2 + 9</gadget>
<output>11</output>

<result>11</result>