A piece of tablecloth with a side length of 10dm should be embroidered with lace around it. What is the length of the lace in decimeters?
一块边长是10dm的桌布，要在它的四周绣上花边，花边的长是多少分米．
<gadget id="calculator">10 * 4</gadget>
<output>40</output>

<result>40</result>