car drove from Shilu to Haikou. Travel 80 kilometers per hour and arrive at Haikou in 2.4 hours. When returning, travel 76.8 kilometers per hour, how many hours will it take to return to Shilu?
一辆汽车从石碌开往海口．去时每小时行80千米，2.4小时到达海口．返回时每小时行76.8千米，问返回石碌时需要多少小时？
<gadget id="calculator">2.4 / 76.8</gadget>
<output>0.03125</output>

<gadget id="calculator">80 * 0.03125</gadget>
<output>2.5</output>

<result>2.5</result>