Xiaohong reads a book and reads 15 pages every day. After 4 days, there are still 3/5 of the book left. 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(3/5)没看，这本书有多少页？
<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">4 / (2/5)</gadget>
<output>10</output>

<gadget id="calculator">15 * 10</gadget>
<output>150</output>

<result>150</result>