Wang Hua reads an extracurricular reading. He reads 20% of the book on the first day, and the remaining 30% on the second day. There are still 140 pages left. How many pages are there in this extracurricular reading?
王华看一本课外读物，第一天看了这本书的20%，第二天看了剩下的30%，还有140页没有看完，这本课外读物共多少页？
<gadget id="calculator">20 / 100</gadget>
<output>1/5 = around 0.2</output>

<gadget id="calculator">1 - (1/5)</gadget>
<output>4/5 = around 0.8</output>

<gadget id="calculator">30 / 100</gadget>
<output>3/10 = around 0.3</output>

<gadget id="calculator">(4/5) * (3/10)</gadget>
<output>6/25 = around 0.24</output>

<gadget id="calculator">1 - (1/5) - (6/25)</gadget>
<output>14/25 = around 0.56</output>

<gadget id="calculator">140 / (14/25)</gadget>
<output>250</output>

<result>250</result>