The length of a rectangle is 7 cm and the width is 5 cm. What is the perimeter of the rectangle?
一个长方形的长时7厘米，宽是5厘米，这个长方形的周长是多少．
<gadget id="calculator">7 + 5</gadget>
<output>12</output>

<gadget id="calculator">12 * 2</gadget>
<output>24</output>

<result>24</result>