There is a rectangular flower bed, 17 meters long and 4 meters wide. If there is a guardrail around it, how long is the guardrail in meters?
有一个长方形花坛，长17米，宽4米．如果在四周围上护栏，护栏长多少米？
<gadget id="calculator">17 + 4</gadget>
<output>21</output>

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

<result>42</result>