City A to City B is 200 kilometers in total. A car departs from City A at 9:00 am and arrives at City B at 11:00 am. Return from City B at 2:30 in the afternoon and arrive in City A at 5:30. Find the average round-trip speed of the car.
甲城到乙城共200千米，一辆汽车早晨9点从甲城出发，11点到乙城．下午2：30从乙城返回，5：30到达甲城．求这辆汽车的往返的平均速度．
<gadget id="calculator">200 * 2</gadget>
<output>400</output>

<gadget id="calculator">2 + 3</gadget>
<output>5</output>

<gadget id="calculator">400 / 5</gadget>
<output>80</output>

<result>80</result>