If the length of a rectangle is 18 cm and the width is 10 cm, what is the perimeter of the rectangle in cm?
一个长方形的长是18厘米，宽是10厘米，这个长方形的周长是多少厘米．
<gadget id="calculator">18 + 10</gadget>
<output>28</output>

<gadget id="calculator">28 * 2</gadget>
<output>56</output>

<result>56</result>