During the Reading Festival held in our county, Li Hong read a book on the first day (1/5). If she read another 18 pages, the ratio of the number of pages she read to the number of pages she didn’t read was 1:2 ． How many pages does this book have?
在我县开展的读书节活动中，李红看一本书，第一天看了(1/5)，如果再看18页，看的页数和没看的页数的比是1：2．这本书一共有多少页？
<gadget id="calculator">1 + 2</gadget>
<output>3</output>

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

<gadget id="calculator">1 / 5</gadget>
<output>1/5 = around 0.2</output>

<gadget id="calculator">(1/3) - (1/5)</gadget>
<output>2/15 = around 0.133333</output>

<gadget id="calculator">18 / (2/15)</gadget>
<output>135</output>

<result>135</result>