The perimeter of a rectangular garden is 20 meters, the length of this garden is 7 meters, and the width is how many meters.
一个长方形花圃的周长是20米，这个花圃长是7米，宽是多少米．
<gadget id="calculator">20 / 2</gadget>
<output>10</output>

<gadget id="calculator">10 - 7</gadget>
<output>3</output>

<result>3</result>