Xiao Ming reads a book and reads 15 pages every day. After 4 days, 3/5 of the book has not been read. How many pages does this book have?
小明看一本书，每天看15页，4天后还剩全书的(3/5)没有看，问这本书共有多少页？
<gadget id="calculator">15 * 4</gadget>
<output>60</output>

<gadget id="calculator">3 / 5</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>