Zhao Ming reads a book and has already read 72 pages, which happens to be (8/9) of this book. How many pages does this book have?
赵明看一本书，已经看72页，正好是这本书的(8/9)，这本书共有多少页？
<gadget id="calculator">8 / 9</gadget>
<output>8/9 = around 0.888889</output>

<gadget id="calculator">72 / (8/9)</gadget>
<output>81</output>

<result>81</result>