A rectangle has the same perimeter as an equilateral triangle. The length of the rectangle is 12 cm and the width is 6 cm. Find the side length of the equilateral triangle.
一个长方形与一个等边三角形的周长相等，长方形的长是12厘米，宽是6厘米，求等边三角形的边长．
<gadget id="calculator">12 + 6</gadget>
<output>18</output>

<gadget id="calculator">2 / 3</gadget>
<output>2/3 = around 0.666667</output>

<gadget id="calculator">18 * (2/3)</gadget>
<output>12</output>

<result>12</result>