Xiaohong reads a book and reads 15 pages a day. After 4 days, 60% of the book is left unread. How many pages does this book have?
小红看一本书，每天看15页，4天后还剩全书的60%没看，这本书有多少页？
<gadget id="calculator">15 * 4</gadget>
<output>60</output>

<gadget id="calculator">60 / 100</gadget>
<output>3/5 = around 0.6</output>

<gadget id="calculator">1 - (3/5)</gadget>
<output>2/5 = around 0.4</output>

<gadget id="calculator">60 / (2/5)</gadget>
<output>150</output>

<result>150</result>