A rectangle is 8 cm long and 5 cm wide, what is the perimeter in cm?
一个长方形，长8厘米，宽5厘米，周长是多少厘米．
<gadget id="calculator">8 + 5</gadget>
<output>13</output>

<gadget id="calculator">13 * 2</gadget>
<output>26</output>

<result>26</result>