From Taicheng to Wencun, among them (4/5) are flat roads, and the rest are uphill and downhill roads. A car goes back and forth from Taicheng to Wencun, traveling a total of 10 kilometers downhill. How many kilometers is the flat road?
从台城到汶村，其中(4/5)是平路，其余是上坡和下坡路．一辆汽车从台城到汶村往返一趟，共行10千米下坡路．平路是多少千米？
<gadget id="calculator">4 / 5</gadget>
<output>4/5 = around 0.8</output>

<gadget id="calculator">1 - (4/5)</gadget>
<output>1/5 = around 0.2</output>

<gadget id="calculator">10 / (1/5)</gadget>
<output>50</output>

<gadget id="calculator">50 * (4/5)</gadget>
<output>40</output>

<result>40</result>