Xiaohong reads a story book, and reads (2/5) of this book in 4 days, and reads exactly 84 pages. How many pages does this story book have?
小红看一本故事书，4天看了这本书的(2/5)，正好看了84页，这本故事书共有多少页？
<gadget id="calculator">2 / 5</gadget>
<output>2/5 = around 0.4</output>

<gadget id="calculator">84 / (2/5)</gadget>
<output>210</output>

<result>210</result>