A and B complete a project independently, team A needs 20 days, and team B needs 30 days. After a few days of cooperation between A and B, team B calls out and assigns another task. The project took 18 days to complete. How many days did Team B call out?
甲、乙单独做完一项工程，甲队须要20天，乙队需要30天．在甲、乙合作若干天后，乙队调出另分配任务．这项工程前后共用18天完成．求乙队调出了多少天？
<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 - (9/10)</gadget>
<output>1/10 = around 0.1</output>

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

<gadget id="calculator">(1/10) / (1/30)</gadget>
<output>3</output>

<gadget id="calculator">18 - 3</gadget>
<output>15</output>

<result>15</result>