The distance between A and B is 720km, and a bus traveled 400km in the first 5 hours. According to this calculation, how many hours will it take to complete the remaining distance? (Solution by proportional method)
甲乙两地相距720km，一辆客车前5小时行了400km．照这样计算，剩下的路程还要多少小时才能行完？(用比例方法解)
<gadget id="calculator">720 - 400</gadget>
<output>320</output>

<gadget id="calculator">400 / 5</gadget>
<output>80</output>

<gadget id="calculator">320 / 80</gadget>
<output>4</output>

<result>4</result>