A rectangle has a width of 8.5 decimeters and a perimeter of 40 decimeters, what is its length?
一个长方形的宽是8.5分米，周长是40分米，它的长是多少分米？
<gadget id="calculator">40 / 2</gadget>
<output>20</output>

<gadget id="calculator">20 - 8.5</gadget>
<output>11.5</output>

<result>11.5</result>