What is the perimeter of a rectangle whose length is 9 cm and is 3 cm greater than its width?
一个长方形长9cm，比宽多3cm，它的周长是多少．
<gadget id="calculator">9 - 3</gadget>
<output>6</output>

<gadget id="calculator">6 + 9</gadget>
<output>15</output>

<gadget id="calculator">15 * 2</gadget>
<output>30</output>

<result>30</result>