Dongdong went to bed at 9:00 p.m. and woke up at 6:00 a.m. the next morning. How many hours did she sleep in total?
冬冬晚上9时睡觉，第二天早上6时起床，她共睡了多少小时
<gadget id="calculator">3 + 6</gadget>
<output>9</output>

<result>9</result>