What is the perimeter of a rectangle whose length is 9 cm and whose width is 3 cm less than its length?
一个长方形长9厘米，宽比长少3厘米，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>