Tongtong reads an extra-curricular book. On the first day, she reads (2/5) of the whole book. If she reads another 12 pages, she just finishes half of the book. How many pages does this extra-curricular book have?
彤彤读一本课外书，第一天读了全书的(2/5)，如果再读12页，恰好读完这本书的一半，这本课外书共有多少页？
<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>