A convoy transported a batch of disaster relief supplies, traveled 40 kilometers per hour, and arrived at the disaster area in 7.5 hours. When returning, travel 50 kilometers per hour, how long will it take to return to the starting point? (Solve with ratio)
某车队运送一批救灾物资，去时每小时行40千米，7.5小时到达灾区．回来时每小时行50千米，多长时间能够返回出发地点？(用比例解)
<gadget id="calculator">40 * 7.5</gadget>
<output>300</output>

<gadget id="calculator">300 / 50</gadget>
<output>6</output>

<result>6</result>