Trees were planted on the side of a road, from the beginning to the end, a total of 16 trees were planted, with an interval of 15 meters between each two. How long is this road?
在一条道路的一旁种树，从头到尾地种，一共种了16棵树，每两棵间隔15米．这条路有多长？
<gadget id="calculator">16 - 1</gadget>
<output>15</output>

<gadget id="calculator">15 * 15</gadget>
<output>225</output>

<result>225</result>