Xiaoqiang planned to read a 180-page novel in 12 days, but actually read 5 pages more than planned every day. According to this calculation, how many days did it take to finish this book less than planned?
小强计划用12天看一本180页的小说，实际每天比计划多看5页，照这样计算，看完这本书比计划少用了多少天？
<gadget id="calculator">180 / 12</gadget>
<output>15</output>

<gadget id="calculator">15 + 5</gadget>
<output>20</output>

<gadget id="calculator">180 / 20</gadget>
<output>9</output>

<gadget id="calculator">12 - 9</gadget>
<output>3</output>

<result>3</result>