In a 5-storey tower, 2 lights are installed on the top floor, and 4 lights are installed on each lower floor. How many lights are installed on the bottom floor? (writing process)
一座5层高的塔，最上边一层装了2只灯，往下每低一层多装4只灯，最下面一层要装多少只灯？(写出过程)
<gadget id="calculator">5 - 1</gadget>
<output>4</output>

<gadget id="calculator">4 * 4</gadget>
<output>16</output>

<gadget id="calculator">16 + 2</gadget>
<output>18</output>

<result>18</result>