The convoy delivered relief supplies to the disaster area. It traveled 60 kilometers per hour when going there, arrived in 4.5 hours, and traveled an extra 15 kilometers per hour when returning. How long did it take to return to the starting point? (Solve with ratio)
车队向灾区运送救灾物资，去时每小时行60千米，4.5小时到达，返回时每小时多行15千米，返回出发地点用了多长时间？(用比例解)
<gadget id="calculator">60 * 4.5</gadget>
<output>270</output>

<gadget id="calculator">15 + 60</gadget>
<output>75</output>

<gadget id="calculator">270 / 75</gadget>
<output>18/5 = around 3.6</output>

<result>18/5 = around 3.6</result>