A book has been read (3/5), and there are 30 pages left, what is the number of pages in this book?
一本书，已经看了(3/5)，还剩30页，则这本数的页数为多少页．
<gadget id="calculator">3 / 5</gadget>
<output>3/5 = around 0.6</output>

<gadget id="calculator">1 - (3/5)</gadget>
<output>2/5 = around 0.4</output>

<gadget id="calculator">30 / (2/5)</gadget>
<output>75</output>

<result>75</result>