A rectangle is 9 cm wide and its length is 3 cm longer than its width. What is the perimeter of the rectangle in cm?
一个长方形宽9cm，长比宽长3cm，这个长方形的周长是多少cm．
<gadget id="calculator">9 + 9 + 3</gadget>
<output>21</output>

<gadget id="calculator">21 * 2</gadget>
<output>42</output>

<result>42</result>