A rectangle has a perimeter of 50 cm, its length is 15 cm, and its width is in cm.
一个长方形，周长是50厘米，它的长是15厘米，宽是多少厘米．
<gadget id="calculator">50 / 2</gadget>
<output>25</output>

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

<result>10</result>