How many decimeters of lace are needed to sew a circle of lace to a square tablecloth with a side length of 15 decimeters?
要给一块边长为15分米的正方形桌布缝上一圈花边，需要多少分米长的花边？
<gadget id="calculator">15 * 4</gadget>
<output>60</output>

<result>60</result>