Xiaoliang reads a story book, and has read 40% of the whole book, and there are 90 pages left. How many pages are there in this book?
小亮看一本故事书，已经看了全书的40%，还剩下90页没有看，这本书共有多少页？
<gadget id="calculator">40 / 100</gadget>
<output>2/5 = around 0.4</output>

<gadget id="calculator">1 - (2/5)</gadget>
<output>3/5 = around 0.6</output>

<gadget id="calculator">90 / (3/5)</gadget>
<output>150</output>

<result>150</result>