Li Wei went to bed at 9 o'clock in the evening and got up at 7 o'clock the next morning. How many hours did he sleep in total?
李伟晚上9时睡觉，第二天早上7时起床，他一共睡了多少小时．
<gadget id="calculator">12 - 9</gadget>
<output>3</output>

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

<result>10</result>