Two kinds of brine containing 40% salt and 10% brine are mixed to produce 30 grams of brine containing 20% brine, how many grams of brine containing 10% brine is needed?
含盐40%和含盐10%的两种盐水混合成含盐20%的盐水30克，那么含盐10%的盐水需要多少克．
<gadget id="calculator">12 - 6</gadget>
<output>6</output>

<gadget id="calculator">40 / 100</gadget>
<output>2/5 = around 0.4</output>

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

<gadget id="calculator">(2/5) - (1/10)</gadget>
<output>3/10 = around 0.3</output>

<gadget id="calculator">6 / (3/10)</gadget>
<output>20</output>

<result>20</result>