The perimeter of a rectangle is 30 cm, its length is 10 cm, and its width is in cm.
一个长方形的周长是30厘米，它的长是10厘米，宽是多少厘米．
<gadget id="calculator">30 / 2</gadget>
<output>15</output>

<gadget id="calculator">15 - 10</gadget>
<output>5</output>

<result>5</result>