There are two sections of uphill and downhill between A and B. It takes 4.5 hours for a person to ride an electric bicycle from A to B, and 3.5 hours to return. If the uphill travel is 12 kilometers per hour , 20 kilometers per hour when going downhill, so how many kilometers are the distance between A and B?
A、B两地之间有上坡和下坡两段路程，某人骑电动车从A地到B地用了4.5小时，返回时用了3.5小时，若上坡时每小时行12千米，下坡时每小时行20千米，那么A、B两地相距多少千米？
<gadget id="calculator">3.5 + 4.5</gadget>
<output>8</output>

<gadget id="calculator">1 / 12</gadget>
<output>1/12 = around 0.083333</output>

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

<gadget id="calculator">(1/12) + (1/20)</gadget>
<output>2/15 = around 0.133333</output>

<gadget id="calculator">8 / (2/15)</gadget>
<output>60</output>

<result>60</result>