The length of a rectangle is 2.1 meters and the width is 1.3 meters. What is its perimeter?
一个长方形的长是2.1米，宽是1.3米，它的周长是多少．
<gadget id="calculator">2.1 + 1.3</gadget>
<output>3.4</output>

<gadget id="calculator">3.4 * 2</gadget>
<output>6.8</output>

<result>6.8</result>