car and a large truck meet on a 9-kilometer-long narrow road, and they must back up to continue. It is known that the speed of the small car is three times the speed of the large truck, the speed of the two vehicles in reverse is 1/5 of their respective speeds, and the distance required for the small car to reverse is four times that of the large truck. If the speed of the car is 50 km/h, how long will it take for both cars to pass through this narrow road?
一辆小汽车与一辆大卡车在一段9千米长的狭路上相遇，必须倒车才能继续通行．已知小汽车的速度是大卡车速度的3倍，两车倒车的速度是各自速度的(1/5)，小汽车需倒车的路程是大卡车需倒车路程的4倍．如果小汽车的速度是50千米/时，那么两车都通过这段狭路最少用多长时间？
<gadget id="calculator">4 + 1</gadget>
<output>5</output>

<gadget id="calculator">4 / 5</gadget>
<output>4/5 = around 0.8</output>

<gadget id="calculator">1 / 5</gadget>
<output>1/5 = around 0.2</output>

<gadget id="calculator">50 * (1/5)</gadget>
<output>10</output>

<gadget id="calculator">(4/5) / 10</gadget>
<output>2/25 = around 0.08</output>

<gadget id="calculator">9 * (2/25)</gadget>
<output>18/25 = around 0.72</output>

<gadget id="calculator">9 / 50</gadget>
<output>9/50 = around 0.18</output>

<gadget id="calculator">(18/25) + (9/50)</gadget>
<output>9/10 = around 0.9</output>

<result>9/10 = around 0.9</result>