Draw the largest circle in a rectangle whose length is 10dm and width is 7dm. What is the circumference of the circle in dm?
在一个长为10dm，宽为7dm的长方形中画一个最大的圆，圆的周长是多少dm．
<gadget id="calculator">3.14 * 7</gadget>
<output>21.98</output>

<result>21.98</result>