The perimeter of a rectangle is 30 cm, and the length is twice the width. What is the area of the rectangle?
一个长方形的周长是30厘米，长是宽的2倍，这个长方形的面积是多少平方厘米？
<gadget id="calculator">1 + 2</gadget>
<output>3</output>

<gadget id="calculator">30 / 2 / 3</gadget>
<output>5</output>

<gadget id="calculator">5 * 2 * 5 * 1</gadget>
<output>50</output>

<result>50</result>