The perimeter of a rectangle is 50 cm, its length is 20 cm, what is its width in cm?
一个长方形的周长是50厘米，它的长是20厘米，宽是多少厘米？
<gadget id="calculator">50 / 2</gadget>
<output>25</output>

<gadget id="calculator">25 - 20</gadget>
<output>5</output>

<result>5</result>