To build a canal, 40% of the total length was built on the first day, and 140 meters on the second day. At this time, the ratio of the remaining length to the length already repaired is 1:3. How long is this canal in meters?
修一条水渠，第一天修了全长的40%，第二天修了140米，这时剩下的与已修的长度比是1：3，这条水渠长多少米？
<gadget id="calculator">1 + 3</gadget>
<output>4</output>

<gadget id="calculator">3 / 4</gadget>
<output>3/4 = around 0.75</output>

<gadget id="calculator">40 / 100</gadget>
<output>2/5 = around 0.4</output>

<gadget id="calculator">(3/4) - (2/5)</gadget>
<output>7/20 = around 0.35</output>

<gadget id="calculator">140 / (7/20)</gadget>
<output>400</output>

<result>400</result>