When building a road, when it reaches the full length (1/3), there is still 20 kilometers away from the midpoint of the road. How many kilometers have been repaired?
修一条公路，当修到全长的(1/3)处时，距离这条公路的中点还有20千米，已经修了多少千米？
<gadget id="calculator">1 / 2</gadget>
<output>1/2 = around 0.5</output>

<gadget id="calculator">1 / 3</gadget>
<output>1/3 = around 0.333333</output>

<gadget id="calculator">(1/2) - (1/3)</gadget>
<output>1/6 = around 0.166667</output>

<gadget id="calculator">20 / (1/6)</gadget>
<output>120</output>

<gadget id="calculator">120 * (1/3)</gadget>
<output>40</output>

<result>40</result>