A car goes from city A to city B. It takes 2 hours on the expressway at a speed of 90 km/h. It takes 3 hours to return on an ordinary road. What is the speed in kilometers when returning?
一辆从A城去B城，去时走高速公路的速度是90千米/时，用了2小时；回来走普通公路，用了3小时，返回时的速度是多少千米？
<gadget id="calculator">2 / 3</gadget>
<output>2/3 = around 0.666667</output>

<gadget id="calculator">90 * (2/3)</gadget>
<output>60</output>

<result>60</result>