A project can be completed by team A alone in 10 days and by team B in 15 days. Now Team A and Team B are working together, and Team A has left for several days because of other tasks in the middle, so it took 9 days to complete the whole project. How many days did Team A leave halfway?
一项工程，甲队单独做10天完工，乙队单独做15完工．现在甲、乙两队合作，中途甲队因有其他任务曾经离开过若干天，这样共用了9天才完成全部工程．甲队中途离开了多少天．
<gadget id="calculator">9 / 15</gadget>
<output>3/5 = around 0.6</output>

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

<gadget id="calculator">1 / 10</gadget>
<output>1/10 = around 0.1</output>

<gadget id="calculator">(2/5) / (1/10)</gadget>
<output>4</output>

<gadget id="calculator">9 - 4</gadget>
<output>5</output>

<result>5</result>