The highway from a county to the provincial capital is 320 kilometers long, and the ordinary road is 450 kilometers long. A car travels at a speed of 80 km/h on an expressway and at 50 km/h on an ordinary road. How much time does it save to travel from the county town to the provincial capital by taking the expressway instead of taking the ordinary road?
某县城到省城的高速公路长320千米，普通公路长450千米．一辆汽车走高速公路的速度是80千米/时，走普通公路的速度是50千米/时，从县城到省城走高速公路比走普通公路节省多少时间？
<gadget id="calculator">450 / 50</gadget>
<output>9</output>

<gadget id="calculator">320 / 80</gadget>
<output>4</output>

<gadget id="calculator">9 - 4</gadget>
<output>5</output>

<result>5</result>