A square handkerchief has a side length of 3 decimeters, and a circle of lace around the side, how many decimeters is the length of the lace.
一块正方形手帕边长3分米，在边上围一圈花边，花边长多少分米．
<gadget id="calculator">3 * 4</gadget>
<output>12</output>

<result>12</result>