To build a section of expressway, the full length (3/5) was built on the first day, and (1/4) the full length was built on the second day, and (7/10) kilometers less was repaired on the second day than on the first day. How long is this highway in kilometers?
修一段高速公路，第一天修了全长的(3/5)，第二天修了全长的(1/4)，第二天比第一天少修(7/10)千米．这段高速公路全长多少千米？
<gadget id="calculator">7 / 10</gadget>
<output>7/10 = around 0.7</output>

<gadget id="calculator">3 / 5</gadget>
<output>3/5 = around 0.6</output>

<gadget id="calculator">1 / 4</gadget>
<output>1/4 = around 0.25</output>

<gadget id="calculator">(3/5) - (1/4)</gadget>
<output>7/20 = around 0.35</output>

<gadget id="calculator">(7/10) / (7/20)</gadget>
<output>2</output>

<result>2</result>