Wang Jun reads a story book and reads 15 pages every day. After 4 days, he reads 20% of the whole book. At this time, there are only 1/5 of the whole book left. How many pages does this storybook have?
王军看一本故事书，每天看15页，看了4天后，又看了全书的20%，这时还剩下全书的(1/5)没看．这本故事书有多少页？
<gadget id="calculator">15 * 4</gadget>
<output>60</output>

<gadget id="calculator">20 / 100</gadget>
<output>1/5 = around 0.2</output>

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

<gadget id="calculator">1 - (1/5) - (1/5)</gadget>
<output>3/5 = around 0.6</output>

<gadget id="calculator">60 / (3/5)</gadget>
<output>100</output>

<result>100</result>