The ratio of copper to zinc in an alloy is 2:3, now there are 6 grams of zinc, how much copper must be used to make an alloy that meets the requirements?
一种合金内铜和锌的比是2：3，现在有6克锌，必须用多少铜才能配制成符合要求的合金？
<gadget id="calculator">2 / 3</gadget>
<output>2/3 = around 0.666667</output>

<gadget id="calculator">6 * (2/3)</gadget>
<output>4</output>

<result>4</result>