There is a pile of feed in the farm. It can be eaten for 12 days only for chickens, and 15 days for ducks. If this pile of feed is given to ducks for 6 days first, and the rest is fed to chickens and ducks, it can be eaten for a few days. ?
饲养场有一堆饲料，只给鸡吃可以吃12天，只给鸭吃可以吃15天，如果把这堆饲料先给鸭吃6天，剩下的给鸡、鸭一起吃，可以吃几天？
<gadget id="calculator">1 / 15</gadget>
<output>1/15 = around 0.066667</output>

<gadget id="calculator">(1/15) * 6</gadget>
<output>2/5 = around 0.4</output>

<gadget id="calculator">1 - (2/5)</gadget>
<output>3/5 = around 0.6</output>

<gadget id="calculator">1 / 12</gadget>
<output>1/12 = around 0.083333</output>

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

<gadget id="calculator">(3/5) / (3/20)</gadget>
<output>4</output>

<result>4</result>