From city A to city B, (3/4) is a flat road, and the rest are uphill and downhill. A car goes back and forth between A and B cities, traveling a total of 20 kilometers uphill. How many kilometers are there between A and B?
从A城到B城，(3/4)是平路，其余是上坡路和下坡路．一辆汽车在A，B两城之间往返一趟，共行驶20千米的上坡路．A，B两城相距多少千米？
<gadget id="calculator">3 / 4</gadget>
<output>3/4 = around 0.75</output>

<gadget id="calculator">1 - (3/4)</gadget>
<output>1/4 = around 0.25</output>

<gadget id="calculator">20 / (1/4)</gadget>
<output>80</output>

<result>80</result>