A rectangle has a length of 15 cm and a width of 9 cm. What is its circumference in centimeters?
一个长方形的长是15厘米，宽9厘米．它的周长是多少厘米？
<gadget id="calculator">15 + 9</gadget>
<output>24</output>

<gadget id="calculator">24 * 2</gadget>
<output>48</output>

<result>48</result>