It takes 20 days for the first team and 30 days for the second team to repair a section of the distance alone. After a few days of cooperation between the first and second teams, the second team is on standby. The project took 18 days to complete. How many days does the second team stop working?
单独修一段路程，一队需用20天，二队需用30天，一、二队合作一些天后，二队停工待命．这项工程前后共用18天完成．求二队停工多少天．
<gadget id="calculator">1 / 20</gadget>
<output>1/20 = around 0.05</output>

<gadget id="calculator">(1/20) * 18</gadget>
<output>9/10 = around 0.9</output>

<gadget id="calculator">1 / 30</gadget>
<output>1/30 = around 0.033333</output>

<gadget id="calculator">(1/30) * 18</gadget>
<output>3/5 = around 0.6</output>

<gadget id="calculator">(3/5) - 1</gadget>
<output>-2/5 = around -0.4</output>

<gadget id="calculator">(9/10) + (-2/5)</gadget>
<output>1/2 = around 0.5</output>

<gadget id="calculator">(1/2) / (1/30)</gadget>
<output>15</output>

<result>15</result>