car travels from city A to city B. It takes 2 hours on the expressway at a speed of 90 km/h. On the way back, it takes 3 hours on an ordinary road at a speed of 70 km/h. How many kilometers more than walking at high speed.
一辆汽车从A城去B城，走高速公路的速度是90千米/小时，用了2小时，公路返回时走普通公路的速度是70千米/小时，用了3小时，走普通公路比走高速多走多少千米．
<gadget id="calculator">70 * 3</gadget>
<output>210</output>

<gadget id="calculator">90 * 2</gadget>
<output>180</output>

<gadget id="calculator">210 - 180</gadget>
<output>30</output>

<result>30</result>