The fuel carried by an aircraft can be used for up to 6.5 hours. When the aircraft flies out, it is downwind and the speed is 1400 km/h, and when it comes back, it is against the wind and the speed is 1200 km/h. Need to fly back?
一架飞机所带的燃料最多可以用6.5小时，飞机飞出去时为顺风，速度为1400千米/时，回来为逆风，速度为1200千米/时，这架飞机最多飞出多少千米就需要往回飞？
<gadget id="calculator">1_400 * 3</gadget>
<output>4_200</output>

<result>4_200</result>