A willow tree is placed every 3 meters between the two buildings. There are 3 willow trees in total. What is the distance between the two buildings in meters?
在两幢大楼之间每隔3米载一棵柳树，共载了3棵，这两幢大楼之间的距离应该是多少米
<gadget id="calculator">3 + 1</gadget>
<output>4</output>

<gadget id="calculator">4 * 3</gadget>
<output>12</output>

<result>12</result>