There are 11 liters of pure alcohol in container A and 15 liters of water in container B. For the first time, part of the pure alcohol in container A is poured into container B to mix the alcohol and water. For the second time, part of the mixture in container B is poured into container A. In this way, the content of pure alcohol in container A is 62.5%, and the content of pure alcohol in container B is 25%. Then how many liters of water need to be poured into container B to make the content of pure alcohol in container B be 10%.
甲容器中有纯酒精11升，乙容器中有水15升，第一次将甲容器中一部分纯酒精倒入乙容器，使酒精与水混合．第二次将乙容器中一部分混合液倒入甲容器．这样，甲容器中纯酒精的含量为62.5%，乙容器中纯酒精的含量为25%．那么需要往乙容器中倒入多少升的水才能使乙容器中纯酒精的含量为10%．
<gadget id="calculator">25 / 100</gadget>
<output>1/4 = around 0.25</output>

<gadget id="calculator">1 - (1/4)</gadget>
<output>3/4 = around 0.75</output>

<gadget id="calculator">15 / (3/4)</gadget>
<output>20</output>

<gadget id="calculator">100 / 100</gadget>
<output>1</output>

<gadget id="calculator">62.5 / 100</gadget>
<output>0.625</output>

<gadget id="calculator">1 - 0.625</gadget>
<output>0.375</output>

<gadget id="calculator">20 - 15</gadget>
<output>5</output>

<gadget id="calculator">11 - 5</gadget>
<output>6</output>

<gadget id="calculator">0.625 - (1/4)</gadget>
<output>0.375</output>

<gadget id="calculator">6 / 0.375</gadget>
<output>16</output>

<gadget id="calculator">0.375 * 16</gadget>
<output>6</output>

<gadget id="calculator">20 - 6</gadget>
<output>14</output>

<gadget id="calculator">14 * (1/4)</gadget>
<output>7/2 = around 3.5</output>

<gadget id="calculator">10 / 100</gadget>
<output>1/10 = around 0.1</output>

<gadget id="calculator">14 * (1/10)</gadget>
<output>7/5 = around 1.4</output>

<gadget id="calculator">(7/2) - (7/5)</gadget>
<output>21/10 = around 2.1</output>

<gadget id="calculator">(21/10) / (1/10)</gadget>
<output>21</output>

<result>21</result>