The convoy transported a batch of relief materials to the disaster area, traveled 80km per hour, and reached the disaster area in 5 hours. Traveling 100km per hour when returning, how long will it take for this convoy to return to the starting point?
车队向灾区运送一批救灾物资，去时每小时行80km，5小时到达灾区．回来时每小时行100km，这支车队要多长时间能够返回出发地？
<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>