A car transports a carload of goods to a certain wharf, and travels 320 kilometers in the first 4 hours. According to this calculation, it can reach the wharf by driving another 400 kilometers at the same speed. How many hours did it take the car to deliver the goods to the dock?
一辆汽车运一车货物到某码头，前4小时行了320千米，照这样计算，用同样的速度再行驶400千米就能到达码头．这辆汽车把货物送到码头，一共行驶了多少小时？
<gadget id="calculator">320 / 4</gadget>
<output>80</output>

<gadget id="calculator">400 / 80</gadget>
<output>5</output>

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

<result>9</result>