When Xiaoqiang reads a story book, the ratio of the number of pages he read to the total number of pages on the first day is 1:3. If he reads another 90 pages, the ratio of the number of pages he has read to the number of pages he has not read is 1:1. How many pages are there?
小强看一本故事书，第一天看的页数与总页数的比是1：3，如果再看90页，已看页数和未看页数的比是1：1，这本书共多少页？
<gadget id="calculator">1 + 1</gadget>
<output>2</output>

<gadget id="calculator">1 / 2</gadget>
<output>1/2 = around 0.5</output>

<gadget id="calculator">1 / 3</gadget>
<output>1/3 = around 0.333333</output>

<gadget id="calculator">(1/2) - (1/3)</gadget>
<output>1/6 = around 0.166667</output>

<gadget id="calculator">90 / (1/6)</gadget>
<output>540</output>

<result>540</result>