Read a book every hour, read half and 10 pages on the first day, read the remaining half and 20 pages on the second day, read the remaining half and 30 pages on the third day, and have 40 pages left. How many pages does this book have.
小时读一本书，第一天读了一半又10页，第二天读了剩下的一半又20页，第三天读了剩下的一半又30页，还剩40页．这本书有多少页．
<gadget id="calculator">40 + 30</gadget>
<output>70</output>

<gadget id="calculator">70 * 2</gadget>
<output>140</output>

<gadget id="calculator">140 + 20</gadget>
<output>160</output>

<gadget id="calculator">160 * 2</gadget>
<output>320</output>

<gadget id="calculator">320 + 10</gadget>
<output>330</output>

<gadget id="calculator">330 * 2</gadget>
<output>660</output>

<result>660</result>