Xiaolan reads a book. On the first day, she reads (2/5) of this book, and on the second day, she reads 30 pages, which is exactly half of the book. How many pages does this book have?
小兰看一本书，第一天看了这本书的(2/5)，第二天看了30页，正好看到这本书的一半，这本书一共有多少页？
<gadget id="calculator">1 / 2</gadget>
<output>1/2 = around 0.5</output>

<gadget id="calculator">2 / 5</gadget>
<output>2/5 = around 0.4</output>

<gadget id="calculator">(1/2) - (2/5)</gadget>
<output>1/10 = around 0.1</output>

<gadget id="calculator">30 / (1/10)</gadget>
<output>300</output>

<result>300</result>