rectangle has a length of 10dm and a width of 8dm, what is its perimeter in dm
一个长方形，长10dm，宽8dm，它的周长是多少dm
<gadget id="calculator">10 + 8</gadget>
<output>18</output>

<gadget id="calculator">18 * 2</gadget>
<output>36</output>

<result>36</result>