Xiaoming has 21 books, which is 7/9 of Xiaohong's. How many books does Xiaohong have?
小明有书21本，是小红的本数的(7/9)，小红有多少本书？
<gadget id="calculator">7 / 9</gadget>
<output>7/9 = around 0.777778</output>

<gadget id="calculator">21 / (7/9)</gadget>
<output>27</output>

<result>27</result>