A rectangle is 10 cm long and 5 cm wide, what is its perimeter in cm?
一个长方形长是10厘米，宽是5厘米，它的周长是多少厘米．
<gadget id="calculator">10 + 5</gadget>
<output>15</output>

<gadget id="calculator">15 * 2</gadget>
<output>30</output>

<result>30</result>