Fangfang read a novel. She read 40 pages on the first day. From the second day on, she read 5 pages more than the previous day. On the last day, she read 80 pages, which was just finished. How many pages does this book have?
芳芳读一本长篇小说，她第一天读40页，从第二天起，每天读的页数都比前一天多5页，最后一天读80页，正好读完．这本书共有多少页？
<gadget id="calculator">40 + 80</gadget>
<output>120</output>

<gadget id="calculator">80 - 40</gadget>
<output>40</output>

<gadget id="calculator">40 / 5</gadget>
<output>8</output>

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

<gadget id="calculator">9 / 2</gadget>
<output>9/2 = around 4.5</output>

<gadget id="calculator">120 * (9/2)</gadget>
<output>540</output>

<result>540</result>