Xiao Ming finished reading a storybook in two days (7/10), the ratio of the number of pages read on the first day to the second day is 3:2. Given that you read 21 pages on the first day, how many pages are there in this book?
小明两天读完一本故事书的(7/10)，第一天和第二天所读页数的比是3：2．已知第一天读了21页，这本书有多少页？
<gadget id="calculator">3 + 2</gadget>
<output>5</output>

<gadget id="calculator">3 / 5</gadget>
<output>3/5 = around 0.6</output>

<gadget id="calculator">7 / 10</gadget>
<output>7/10 = around 0.7</output>

<gadget id="calculator">(3/5) * (7/10)</gadget>
<output>21/50 = around 0.42</output>

<gadget id="calculator">21 / (21/50)</gadget>
<output>50</output>

<result>50</result>