If a rectangle is 5 cm long and 3 cm wide, what is its perimeter in cm?
一个长方形的长5厘米，宽3厘米，它的周长多少厘米．
<gadget id="calculator">5 + 3</gadget>
<output>8</output>

<gadget id="calculator">8 * 2</gadget>
<output>16</output>

<result>16</result>