Li Wei reads a story book. He read the whole book (1/4) on the first day, and 40% of the whole book on the second day, leaving 21 pages unread. How many pages does this storybook have?
李伟看一本故事书，第一天看了全书的(1/4)，第二天看了全书的40%，还剩下21页没有看．这本故事书共有多少页？
<gadget id="calculator">1 / 4</gadget>
<output>1/4 = around 0.25</output>

<gadget id="calculator">40 / 100</gadget>
<output>2/5 = around 0.4</output>

<gadget id="calculator">1 - (1/4) - (2/5)</gadget>
<output>7/20 = around 0.35</output>

<gadget id="calculator">21 / (7/20)</gadget>
<output>60</output>

<result>60</result>