The distance between A and B is 12 kilometers. It takes 3 hours for a car to drive from A to B, and an extra hour to return. Find the average speed of the car going back and forth.
甲、乙两地相距12千米，一辆汽车从甲地驶往乙地用了3小时，返回时多用了1小时，求这辆汽车往返的平均速度．
<gadget id="calculator">12 * 2</gadget>
<output>24</output>

<gadget id="calculator">3 + 1 + 3</gadget>
<output>7</output>

<gadget id="calculator">24 / 7</gadget>
<output>24/7 = around 3.428571</output>

<result>24/7 = around 3.428571</result>