A rectangular garden is 20 meters long and 9 meters wide. What is its circumference.
一个长方形花园，长20米，宽9米．它的周长是多少．
<gadget id="calculator">20 + 9</gadget>
<output>29</output>

<gadget id="calculator">29 * 2</gadget>
<output>58</output>

<result>58</result>