The Changshun engineering team completed a canal in three days. On the first day, 25% of the total length was repaired. The ratio between the second day and the third day was 7:8. The first day was 21m less than the third day. How long is this canal in meters?
长顺工程队三天修完一条水渠，第一天修了全长的25%，第二天与第三天修的比是7：8，第一天修的比第三天修的少21m，这条水渠全长多少米？
<gadget id="calculator">7 / 8</gadget>
<output>7/8 = around 0.875</output>

<gadget id="calculator">21 * (7/8)</gadget>
<output>147/8 = around 18.375</output>

<gadget id="calculator">21 + (147/8)</gadget>
<output>315/8 = around 39.375</output>

<gadget id="calculator">25 / 100</gadget>
<output>1/4 = around 0.25</output>

<gadget id="calculator">(1/4) * (7/8)</gadget>
<output>7/32 = around 0.21875</output>

<gadget id="calculator">1 - (1/4) - (7/32) - (1/4)</gadget>
<output>9/32 = around 0.28125</output>

<gadget id="calculator">(315/8) / (9/32)</gadget>
<output>140</output>

<result>140</result>