Xiaohua reads a story book, and has already read the whole book (2/5) a few days ago, and after reading 12 pages, he can finish half of the book. How many pages does this storybook have?
小华看一本故事书，前几天已经看了全书的(2/5)，再看12页就能看完这本书的一半．这本故事书一共有多少页？
<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">12 / (1/10)</gadget>
<output>120</output>

<result>120</result>