The convoy transported a batch of relief supplies to the disaster area, traveled 60km per hour and arrived in 4.5 hours. When coming back, travel 75km per hour. How long did it take to return?
车队向灾区运送一批救灾物资，去时每小时行60km，4.5小时到达．回来时每小时行75km．返回时用了多长时间？
<gadget id="calculator">4.5 / 75</gadget>
<output>0.06</output>

<gadget id="calculator">60 * 0.06</gadget>
<output>3.6</output>

<result>3.6</result>