A section of road with a length of 324 meters was built. A total of 240 meters were built in the first 8 hours, and the remaining 21 meters were repaired every hour. How many hours will it take to complete the repair?
修一段长324米的路，前8小时共修了240米，剩下的每小时修21米，还要几小时才能修完？
<gadget id="calculator">324 - 240</gadget>
<output>84</output>

<gadget id="calculator">84 / 21</gadget>
<output>4</output>

<result>4</result>