The area of a rectangular painting is 8.4 square decimeters and its length is 3.5 decimeters. What is its perimeter?
一幅长方形画的面积是8.4平方分米，长是3.5分米，它的周长是多少分米？
<gadget id="calculator">8.4 / 3.5</gadget>
<output>2.4</output>

<gadget id="calculator">8.4 + 2.4</gadget>
<output>10.8</output>

<gadget id="calculator">10.8 * 2</gadget>
<output>21.6</output>

<result>21.6</result>