Zhang Village dug a canal, dug the full length (1/5) on the first day, and dug the full length (1/4) on the second day. It is known that the excavation was 40m less on the first day than on the second day. What is the total length of this canal?
张村挖一条水渠，第一天挖了全长的(1/5)，第二天挖了全长的(1/4)．已知第一天比第二天少挖40m，这条水渠全长多少米？
<gadget id="calculator">1 / 4</gadget>
<output>1/4 = around 0.25</output>

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

<gadget id="calculator">(1/4) - (1/5)</gadget>
<output>1/20 = around 0.05</output>

<gadget id="calculator">40 / (1/20)</gadget>
<output>800</output>

<result>800</result>