A tree is planted every 2 meters between the two buildings, a total of 15 trees are planted, what is the distance between the two buildings in meters?
两栋楼之间每隔2米种一棵树，共种了15棵，这两栋楼之间相距多少米．
<gadget id="calculator">15 + 1</gadget>
<output>16</output>

<gadget id="calculator">2 * 16</gadget>
<output>32</output>

<result>32</result>