reservoir has a certain amount of original water, and the river water enters the reservoir evenly every day. 5 pumps can be drained for 20 consecutive days; 6 identical pumps can be drained for 15 consecutive days. If it is required to drain in 6 days, how many similar pumps are needed?
一水库原有存水量一定，河水每天均匀入库.5台抽水机连续20天可抽干；6台同样的抽水机连续15天可抽干．若要求6天抽干，需要多少台同样的抽水机．
<gadget id="calculator">20 * 5</gadget>
<output>100</output>

<gadget id="calculator">15 * 6</gadget>
<output>90</output>

<gadget id="calculator">100 - 90</gadget>
<output>10</output>

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

<gadget id="calculator">10 / 5</gadget>
<output>2</output>

<gadget id="calculator">2 * 20</gadget>
<output>40</output>

<gadget id="calculator">100 - 40</gadget>
<output>60</output>

<gadget id="calculator">2 * 6</gadget>
<output>12</output>

<gadget id="calculator">60 + 12</gadget>
<output>72</output>

<gadget id="calculator">72 / 6</gadget>
<output>12</output>

<result>12</result>