There is a batch of stock in the warehouse, and the goods will continue to be shipped into the warehouse in the future, and the same amount of goods will be shipped every day. Use the same car to transport the goods out of the warehouse. If 4 cars are used every day, it will be shipped in 9 days; if 5 cars are used every day, it will be shipped in 6 days. If the original inventory in the warehouse is shipped by 1 car, how many days will it take to be shipped?
仓库里原有一批存货，以后继续运货进仓，且每天运进的货一样多．用同样的汽车运货出仓，如果每天用4辆汽车，则9天恰好运完；如果每天用5辆汽车，则6天恰好运完．仓库里原有的存货若用1辆汽车运则需要几天运完？
<gadget id="calculator">4 * 9</gadget>
<output>36</output>

<gadget id="calculator">5 * 6</gadget>
<output>30</output>

<gadget id="calculator">36 - 30</gadget>
<output>6</output>

<gadget id="calculator">9 - 6</gadget>
<output>3</output>

<gadget id="calculator">6 / 3</gadget>
<output>2</output>

<gadget id="calculator">2 * 9</gadget>
<output>18</output>

<gadget id="calculator">36 - 18</gadget>
<output>18</output>

<result>18</result>