Xiaogang reads a storybook, originally planned to finish it in 15 days, but actually reads 10 more pages a day, and finished it 3 days ahead of schedule. How many pages does this book have?
小刚看一本故事书，原计划15天看完，实际每天多看10页，提前3天看完．这本书一共有多少页？
<gadget id="calculator">10 * 15</gadget>
<output>150</output>

<gadget id="calculator">10 * 3</gadget>
<output>30</output>

<gadget id="calculator">150 - 30</gadget>
<output>120</output>

<gadget id="calculator">1 / 15</gadget>
<output>1/15 = around 0.066667</output>

<gadget id="calculator">(1/15) * 3</gadget>
<output>1/5 = around 0.2</output>

<gadget id="calculator">(1/15) * 15</gadget>
<output>1</output>

<gadget id="calculator">(1/5) - 1</gadget>
<output>-4/5 = around -0.8</output>

<gadget id="calculator">1 + (-4/5)</gadget>
<output>1/5 = around 0.2</output>

<gadget id="calculator">120 / (1/5)</gadget>
<output>600</output>

<result>600</result>