For a book, I read 12 pages on the first day, (1/3) on the second day, and read 18 pages on the third day, exactly half of the book. How many pages does this book have?
一本书，第一天看了12页，第二天看了(1/3)，第三天再看18页正好看了这本书的一半．这本书一共有多少页？
<gadget id="calculator">12 + 18</gadget>
<output>30</output>

<gadget id="calculator">1 / 2</gadget>
<output>1/2 = around 0.5</output>

<gadget id="calculator">1 / 3</gadget>
<output>1/3 = around 0.333333</output>

<gadget id="calculator">(1/2) - (1/3)</gadget>
<output>1/6 = around 0.166667</output>

<gadget id="calculator">30 / (1/6)</gadget>
<output>180</output>

<result>180</result>