Xiao Ming reads a book. He reads part of it on the first day. The ratio of the number of pages he has read to the number of pages he has not read is 3:5. On the second day, he reads 42 pages. At this time, the number of pages he has read is the number of pages he has not read. 2 times that of , how many pages does this book have?
小明看一本书，第一天看了一部分，已看页数与未看页数的比为3：5，第二天又看了42页，这时已看的页数是未看页数的2倍，这本书一共有多少页？
<gadget id="calculator">2 + 1</gadget>
<output>3</output>

<gadget id="calculator">2 / 3</gadget>
<output>2/3 = around 0.666667</output>

<gadget id="calculator">3 + 5</gadget>
<output>8</output>

<gadget id="calculator">3 / 8</gadget>
<output>3/8 = around 0.375</output>

<gadget id="calculator">(2/3) - (3/8)</gadget>
<output>7/24 = around 0.291667</output>

<gadget id="calculator">42 / (7/24)</gadget>
<output>144</output>

<result>144</result>