Li Ming reads a book. He reads (1/5) of the whole book on the first day, and reads 39 pages on the second day. At this time, he reads exactly half of the book. How many pages does this book have?
李明看一本书，第一天看了全书的(1/5)，第二天看了39页，这时正好看了全书的一半，这本书共有多少页？
<gadget id="calculator">1 / 2</gadget>
<output>1/2 = around 0.5</output>

<gadget id="calculator">1 / 5</gadget>
<output>1/5 = around 0.2</output>

<gadget id="calculator">(1/2) - (1/5)</gadget>
<output>3/10 = around 0.3</output>

<gadget id="calculator">39 / (3/10)</gadget>
<output>130</output>

<result>130</result>