Xiao Ming reads a story book. The ratio of the number of pages he has read to the number of pages he has not read is 3:5. He has read 21 pages. How many pages are there in total?
小明读一本故事书，已读页数和未读页数的比是3：5，他已经读完21页，这本书一共有多少页？
<gadget id="calculator">3 + 5</gadget>
<output>8</output>

<gadget id="calculator">3 / 8</gadget>
<output>3/8 = around 0.375</output>

<gadget id="calculator">21 / (3/8)</gadget>
<output>56</output>

<result>56</result>