Xiaohong reads a book. She reads (1/5) of the whole book on the first day and (3/8) of the whole book on the second day. At this time, there are 51 pages left. How many pages are there in this book?
小红看一本书，第一天看了全书的(1/5)，第二天看了全书的(3/8)，这时还剩51页没看，这本书一共有多少页？
<gadget id="calculator">1 / 5</gadget>
<output>1/5 = around 0.2</output>

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

<gadget id="calculator">1 - (1/5) - (3/8)</gadget>
<output>17/40 = around 0.425</output>

<gadget id="calculator">51 / (17/40)</gadget>
<output>120</output>

<result>120</result>