What is the perimeter of a rectangle whose length is 12 cm and whose width is 3 cm less than its length?
一个长方形长12厘米，宽比长少3厘米，它的周长是多少．
<gadget id="calculator">12 - 3</gadget>
<output>9</output>

<gadget id="calculator">12 + 9</gadget>
<output>21</output>

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

<result>42</result>