There is a rectangular flower bed with a circumference of 20 meters and a width of 4 meters. What is the length of this rectangular flower bed?
有一个长方形花坛，周长是20米，宽是4米，这个长方形花坛的长是多少米？
<gadget id="calculator">20 / 2</gadget>
<output>10</output>

<gadget id="calculator">10 - 4</gadget>
<output>6</output>

<result>6</result>