Xiaohong reads a book. She reads 20% of the book on the first day, and the remaining 30% on the second day. There are still 84 pages left. How many pages does this book have?
小红看一本书，第一天看了全书的20%，第二天看了剩下的30%，这时还剩下84页没有看．这本书一共有多少页？
<gadget id="calculator">30 / 100</gadget>
<output>3/10 = around 0.3</output>

<gadget id="calculator">1 - (3/10)</gadget>
<output>7/10 = around 0.7</output>

<gadget id="calculator">84 / (7/10)</gadget>
<output>120</output>

<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">120 / (4/5)</gadget>
<output>150</output>

<result>150</result>