If the length of a rectangle is 15 cm and the width is 5 cm shorter than the length, what is the perimeter of the rectangle?
一个长方形的长是15厘米，宽比长短5厘米，这个长方形的周长是多少．
<gadget id="calculator">15 - 5</gadget>
<output>10</output>

<gadget id="calculator">15 + 10</gadget>
<output>25</output>

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

<result>50</result>