The distance between A and B is 340 kilometers. It takes a car 4.5 hours to go there and 4 hours to return. How many kilometers per hour does this car travel between A and B on average?
甲、乙两地相距340千米，一辆汽车去时用了4.5小时，回来时用了4小时，这辆汽车往返甲、乙两地平均每小时行多少千米？
<gadget id="calculator">340 * 2</gadget>
<output>680</output>

<gadget id="calculator">4.5 + 4</gadget>
<output>8.5</output>

<gadget id="calculator">680 / 8.5</gadget>
<output>80</output>

<result>80</result>