In a book, the ratio of the number of pages read to the number of unread pages is 3:7. If you read another 30 pages, then the number of unread pages accounts for (3/2) of the number of pages read. How many are there in this book? Page.
一本书，已读的页数与未读页数的比是3：7，如果再读30页，那么未读的页数占已读页数的(3/2)，这本书共有多少页．
<gadget id="calculator">3 + 2</gadget>
<output>5</output>

<gadget id="calculator">2 / 5</gadget>
<output>2/5 = around 0.4</output>

<gadget id="calculator">3 + 7</gadget>
<output>10</output>

<gadget id="calculator">3 / 10</gadget>
<output>3/10 = around 0.3</output>

<gadget id="calculator">(2/5) - (3/10)</gadget>
<output>1/10 = around 0.1</output>

<gadget id="calculator">30 / (1/10)</gadget>
<output>300</output>

<result>300</result>