There are alcohol solutions A, B, and C. Their pure alcohol content is 40%, 36%, and 35% respectively. It is necessary to prepare 12 liters of alcohol solution with a pure alcohol content of 39%. At least how many liters of type A alcohol should be taken.
有酒精溶液A、B、C，它们的纯酒精含量分别是40%、36%、35%，需配制纯酒精含量为39%的酒精液12升，至少要取A种酒精多少升．
<gadget id="calculator">39 / 100</gadget>
<output>39/100 = around 0.39</output>

<gadget id="calculator">12 * (39/100)</gadget>
<output>117/25 = around 4.68</output>

<gadget id="calculator">36 / 100</gadget>
<output>9/25 = around 0.36</output>

<gadget id="calculator">12 * (9/25)</gadget>
<output>108/25 = around 4.32</output>

<gadget id="calculator">(117/25) - (108/25)</gadget>
<output>9/25 = around 0.36</output>

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

<gadget id="calculator">(2/5) - (9/25)</gadget>
<output>1/25 = around 0.04</output>

<gadget id="calculator">(9/25) / (1/25)</gadget>
<output>9</output>

<result>9</result>