To build a canal, the full length (1/4) was built on the first day, and 210 meters was built on the second day, so that (3/5) of the whole task was completed. How long is this canal in meters?
修一条水渠，第一天修了全长的(1/4)，第二天又修了210米，这样就完成了全部任务的(3/5)，这条水渠长多少米？
<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">210 / (7/20)</gadget>
<output>600</output>

<result>600</result>