An engineering team plans to build a canal in 3 days. On the first day, they built 200 meters, on the second day they built the full length (2/5), and on the third day, they built half of the sum of the previous two days. How long is this canal in meters?
一个工程队计划3天修完一条水渠，第一天修了200米，第二天修了全长的(2/5)，第三天修了前两天总和的一半，这条水渠长多少米？
<gadget id="calculator">200 / 2</gadget>
<output>100</output>

<gadget id="calculator">200 + 100</gadget>
<output>300</output>

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

<gadget id="calculator">(2/5) / 2</gadget>
<output>1/5 = around 0.2</output>

<gadget id="calculator">1 - (2/5) - (1/5)</gadget>
<output>2/5 = around 0.4</output>

<gadget id="calculator">300 / (2/5)</gadget>
<output>750</output>

<result>750</result>