There are some science and art books in the library, of which science and technology books account for (4/5). If 20 science and technology books are replaced by literary and art books, then science and technology books account for all (8/15). How many science and technology books are there? Book?
图书馆里有一些科技书和文艺书，其中科技书占(4/5)，如果用文艺书换走科技书20本，那么科技书占全部的(8/15)，问原来科技书有多少本？
<gadget id="calculator">4 / 5</gadget>
<output>4/5 = around 0.8</output>

<gadget id="calculator">8 / 15</gadget>
<output>8/15 = around 0.533333</output>

<gadget id="calculator">(4/5) - (8/15)</gadget>
<output>4/15 = around 0.266667</output>

<gadget id="calculator">20 / (4/15)</gadget>
<output>75</output>

<gadget id="calculator">75 * (4/5)</gadget>
<output>60</output>

<result>60</result>