To fill a pool of water, it takes 10 hours to open pipe A alone, 12 hours to open pipe B alone, and 15 hours to open pipe C alone. Now the pool is empty. Three water pipes are opened at 8 am, and pipe A is closed in the middle. By 2 pm When to fill up the empty pool, when to close pipe A?
注满一池水，单开甲管要10小时，单开乙管要12小时，单开丙管要15小时，现在是空池，上午8时打开三个水管，中间关闭甲管，到下午2时把空水池注满，问几时关闭甲管？
<gadget id="calculator">1 / 12</gadget>
<output>1/12 = around 0.083333</output>

<gadget id="calculator">1 / 15</gadget>
<output>1/15 = around 0.066667</output>

<gadget id="calculator">(1/12) + (1/15)</gadget>
<output>3/20 = around 0.15</output>

<gadget id="calculator">14 - 8</gadget>
<output>6</output>

<gadget id="calculator">(3/20) * 6</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 / 10</gadget>
<output>1/10 = around 0.1</output>

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

<gadget id="calculator">1 + 8</gadget>
<output>9</output>

<result>9</result>