The fuel carried by an aircraft can be used for the flight of the aircraft for up to 6 hours. For flight training, when going with the wind, the flight is 1500 kilometers per hour; when the return is against the wind, the flight is 1200 meters per hour. How long does the plane fly at most before it has to fly back?
一架飞机所带的燃料，最多可供飞机飞行6小时．进行飞行训练，去时顺风，每小时飞行1500千米；返回时逆风，每小时飞行1200米．飞机最多飞出多长时间，就得往回飞？
<gadget id="calculator">5 + 4</gadget>
<output>9</output>

<gadget id="calculator">4 / 9</gadget>
<output>4/9 = around 0.444444</output>

<gadget id="calculator">6 * (4/9)</gadget>
<output>8/3 = around 2.666667</output>

<result>8/3 = around 2.666667</result>