On both sides of a 120-meter-long tunnel, install a light at an average interval of 15 meters from the beginning to the end (both ends are installed), how many lights need to be installed in total?
在一条长120米的隧道两侧，从头到尾平均每隔15米安装一盏灯(两头都安装)，共需要安装多少盏灯？
<gadget id="calculator">120 / 15</gadget>
<output>8</output>

<gadget id="calculator">8 + 1</gadget>
<output>9</output>

<gadget id="calculator">9 * 2</gadget>
<output>18</output>

<result>18</result>