There is a vegetable garden, which is surrounded by a fence to form an equilateral triangle. One side is 15 meters long. How long is the fence?
有一个菜园，它的外面用篱笆围成了一个等边三角形，其中一条边长是15米，篱笆长是多少米？
<gadget id="calculator">15 * 3</gadget>
<output>45</output>

<result>45</result>