After a highway has been built for 1/3 of its full length, it is still 4 kilometers away from the midpoint. How many kilometers is the total length of this road?
一条公路修了全长的(1/3)后，离中点还有4千米，这条路全长有多少千米．
<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">4 / (1/6)</gadget>
<output>24</output>

<result>24</result>