Cong Cong goes to bed at 9:00 every night and wakes up at 6:00 the next morning. How many hours did he sleep in total?
聪聪每天晚上9：00休息，第二天早晨6：00起床，他一共睡了多少小时．
<gadget id="calculator">24 - 21</gadget>
<output>3</output>

<gadget id="calculator">6 - 0</gadget>
<output>6</output>

<gadget id="calculator">3 + 6</gadget>
<output>9</output>

<result>9</result>