The fuel carried by an airplane can be used for up to 6 hours. The speed of the airplane is 1500km/h when it goes out, and the speed when it returns is 1200km/h. How many kilometers does the airplane have to fly back? (column equation solution)
一架飞机所带的燃料最多可用6h，飞机去时的速度是1500km/h，返回时的速度是1200km/h，这架飞机最多飞出多少千米就要往回飞？(列方程解答)
<gadget id="calculator">1 / 1_500</gadget>
<output>1/1_500 = around 0.000667</output>

<gadget id="calculator">1 / 1_200</gadget>
<output>1/1_200 = around 0.000833</output>

<gadget id="calculator">(1/1_500) + (1/1_200)</gadget>
<output>3/2_000 = around 0.0015</output>

<gadget id="calculator">6 / (3/2_000)</gadget>
<output>4_000</output>

<result>4_000</result>