The convoy transported a batch of materials to the disaster area, with an average of 80km per hour, and arrived in 5 hours. The average increase of 20km per hour when returning, how long will it take for this convoy to return?
车队向灾区运送一批物资，去时平均每小时80km，5小时到达．回来时平均每小时增加了20km，这支车队返回时需要多长时间？
<gadget id="calculator">80 + 20</gadget>
<output>100</output>

<gadget id="calculator">5 / 100</gadget>
<output>1/20 = around 0.05</output>

<gadget id="calculator">80 * (1/20)</gadget>
<output>4</output>

<result>4</result>