What is the perimeter of a rectangle whose length is 15 cm and width is 10 cm?
一个长为15厘米，宽为10厘米的长方形，它的周长是多少厘米．
<gadget id="calculator">15 + 10</gadget>
<output>25</output>

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

<result>50</result>