An airplane flies an average of 420 kilometers per hour. After 1.5 hours, it flies from place A to place B. When it returns to headwind, it flies less (1/7) per hour on average than when it went there. How many hours?
一架飞机平均每小时飞行420千米，经过1.5小时从甲地飞回乙地，返回时逆风，平均每小时比去时少飞行(1/7)，则这架飞机往返甲乙两地一共飞行了多少小时？
<gadget id="calculator">1 / 7</gadget>
<output>1/7 = around 0.142857</output>

<gadget id="calculator">1 - (1/7)</gadget>
<output>6/7 = around 0.857143</output>

<gadget id="calculator">1 / (6/7)</gadget>
<output>7/6 = around 1.166667</output>

<gadget id="calculator">1.5 * (7/6)</gadget>
<output>1.75</output>

<gadget id="calculator">1.75 + 1.5</gadget>
<output>3.25</output>

<result>3.25</result>