To build a canal, the full length (1/6) of the canal was built in 3 days, and another 42 meters were repaired. The number of meters already repaired accounted for 40% of the total length. How long is this canal in meters?
修一条水渠，3天修了全长的(1/6)，再修42米，已修的米数占全长的40%，这条水渠长多少米？
<gadget id="calculator">40 / 100</gadget>
<output>2/5 = around 0.4</output>

<gadget id="calculator">1 / 6</gadget>
<output>1/6 = around 0.166667</output>

<gadget id="calculator">(2/5) - (1/6)</gadget>
<output>7/30 = around 0.233333</output>

<gadget id="calculator">42 / (7/30)</gadget>
<output>180</output>

<result>180</result>