If the length of a rectangle is 20 decimeters and the circumference is 50 decimeters, what is its width?
一个长方形长是20分米，周长是50分米，它的宽是多少分米．
<gadget id="calculator">50 / 2</gadget>
<output>25</output>

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

<result>5</result>