The fuel carried by an aircraft can be used for up to 6 hours. When the aircraft flies to the wind, it can fly 600 kilometers per hour; when it returns to the wind, it can fly 750 kilometers per hour. The plane can fly no more than how many kilometers it needs to return home.
一架飞机所带的燃料最多可用6小时，飞机飞去时逆风，每小时飞行600千米；返回时顺风，每小时飞行750千米．这架飞机最多能飞出多少千米就需返航．
<gadget id="calculator">1 / 600</gadget>
<output>1/600 = around 0.001667</output>

<gadget id="calculator">1 / 750</gadget>
<output>1/750 = around 0.001333</output>

<gadget id="calculator">(1/600) + (1/750)</gadget>
<output>3/1_000 = around 0.003</output>

<gadget id="calculator">6 / (3/1_000)</gadget>
<output>2_000</output>

<result>2_000</result>