The total length of the Shanghai-Nanjing Expressway is 270 kilometers. The truck started from Nanjing and drove to Shanghai along the Shanghai-Nanjing Expressway. It has been traveling for 2 hours at 90 kilometers per hour. How many kilometers does the truck have to travel to Shanghai?
沪宁高速公路全长270千米．卡车从南京出发，沿沪宁高速公路开往上海，已经行了2小时，每小时行90千米．卡车到上海还要行多少千米？
<gadget id="calculator">90 * 2</gadget>
<output>180</output>

<gadget id="calculator">270 - 180</gadget>
<output>90</output>

<result>90</result>