To build a highway with a total length of 30 kilometers, (2/5) is completed in the first quarter, and (3/7) is completed in the second quarter. How many kilometers are left to be repaired?
修一条高速公路，全长30千米，第一季度修完它的(2/5)，第二季度修完它的(3/7)，还剩多少千米没有修？
<gadget id="calculator">2 / 5</gadget>
<output>2/5 = around 0.4</output>

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

<gadget id="calculator">1 - (2/5) - (3/7)</gadget>
<output>6/35 = around 0.171429</output>

<gadget id="calculator">30 * (6/35)</gadget>
<output>36/7 = around 5.142857</output>

<result>36/7 = around 5.142857</result>