A square tablecloth with a side length of 9 decimeters should be embroidered with lace around it. What is the side length of the lace?
一块边长是9分米的正方形桌布，要在它的四周绣上花边，花边的边长是多少分米．
<gadget id="calculator">9 * 4</gadget>
<output>36</output>

<result>36</result>