Uncles of the People’s Liberation Army helped the local residents clean up a section of a sewage river. The ratio of the length of cleaning to the total length of this sewage river on the first day was 3:8. If we cleaned another 80m, we could clean up (1/2) of the total length of this sewage river ． How long is this sewage river?
解放军叔叔帮助驻地居民清理一条污水河的一段，第一天清理的长度与这段污水河总长的比是3：8，如果再清理80m，就可以清理这段污水河总长的(1/2)．这段污水河长多少米？
<gadget id="calculator">1 / 2</gadget>
<output>1/2 = around 0.5</output>

<gadget id="calculator">3 / 8</gadget>
<output>3/8 = around 0.375</output>

<gadget id="calculator">(1/2) - (3/8)</gadget>
<output>1/8 = around 0.125</output>

<gadget id="calculator">80 / (1/8)</gadget>
<output>640</output>

<result>640</result>