The expressway from Shanghai to Guangzhou is 810 kilometers long. The truck starts from Guangzhou and goes to Shanghai. After traveling 540 kilometers, it travels at a speed of 90 kilometers per hour. How many hours will it take for the truck to reach Shanghai?
上海到广州的高速公路全长810千米，卡车从广州出发，开往上海，已经行了540千米以后，以每小时行90千米的速度行驶，卡车到上海还要行几小时？
<gadget id="calculator">810 - 540</gadget>
<output>270</output>

<gadget id="calculator">270 / 90</gadget>
<output>3</output>

<result>3</result>