After building a road, after the full length (3/7) is built, there is still 1.7 kilometers away from the midpoint of the road. Find the length of this road?
修一条公路，修了全长的(3/7)后，离这条公路的中点还有1.7千米，求这条公路的长？
<gadget id="calculator">1 / 2</gadget>
<output>1/2 = around 0.5</output>

<gadget id="calculator">3 / 7</gadget>
<output>3/7 = around 0.428571</output>

<gadget id="calculator">(1/2) - (3/7)</gadget>
<output>1/14 = around 0.071429</output>

<gadget id="calculator">1.7 / (1/14)</gadget>
<output>23.8</output>

<result>23.8</result>