If the length of a rectangle is 15 meters and the width is 10 meters, what is its perimeter?
一个长方形的长是15米，宽是10米，它的周长是多少米
<gadget id="calculator">15 + 10</gadget>
<output>25</output>

<gadget id="calculator">25 * 2</gadget>
<output>50</output>

<result>50</result>