The distance between A and B is 1800 kilometers. A plane flies to B at a speed of 9 kilometers per minute, and the speed when it flies back is 7.2 kilometers per minute. What is the average speed of the plane in kilometers per minute?
甲乙两地相距1800千米，一架飞以机每分钟9千米的速度飞往乙地，飞回时的速度是每分钟7.2千米，飞机的平均速度是每分钟多少千米．
<gadget id="calculator">1_800 * 2</gadget>
<output>3_600</output>

<gadget id="calculator">1_800 / 9</gadget>
<output>200</output>

<gadget id="calculator">1_800 / 7.2</gadget>
<output>250</output>

<gadget id="calculator">200 + 250</gadget>
<output>450</output>

<gadget id="calculator">3_600 / 450</gadget>
<output>8</output>

<result>8</result>