The distance between A and B is 120 kilometers. From A to B, it takes 5 hours to go uphill and then downhill. The uphill speed is 20 kilometers per hour, and the downhill speed is 30 kilometers per hour. How many kilometers did this person walk downhill?
甲、乙两地相距120千米，某从从甲地到乙地，先上坡后下坡，共用5小时，上坡速度为每小时20千米，下坡速度为每小时30千米，此人下坡走了多少千米．
<gadget id="calculator">120 / 20</gadget>
<output>6</output>

<gadget id="calculator">6 - 5</gadget>
<output>1</output>

<gadget id="calculator">1 / 20</gadget>
<output>1/20 = around 0.05</output>

<gadget id="calculator">1 / 30</gadget>
<output>1/30 = around 0.033333</output>

<gadget id="calculator">(1/20) - (1/30)</gadget>
<output>1/60 = around 0.016667</output>

<gadget id="calculator">1 / (1/60)</gadget>
<output>60</output>

<result>60</result>