Xiaohua reads a book and has read 90 pages. The ratio of the number of pages she has read to the number of pages she has not read is 3:4. How many pages are there in this book?
小华看一本书，已看了90页，已看的与未看的页数的比是3：4，这本书一共有多少页？
<gadget id="calculator">90 / 3</gadget>
<output>30</output>

<gadget id="calculator">3 + 4</gadget>
<output>7</output>

<gadget id="calculator">30 * 7</gadget>
<output>210</output>

<result>210</result>