Add some water to 6 kg of 15% brine to reduce the concentration of brine to 10%, how many kg of water should be added?
在6千克浓度为15%的盐水中加入一些水，使盐水的浓度降为10%，应加入多少千克水？
<gadget id="calculator">15 / 100</gadget>
<output>3/20 = around 0.15</output>

<gadget id="calculator">6 * (3/20)</gadget>
<output>9/10 = around 0.9</output>

<gadget id="calculator">(9/10) - 0.6</gadget>
<output>0.3</output>

<gadget id="calculator">0.3 / 0.1</gadget>
<output>3</output>

<result>3</result>