After lending out (11/15) of the total number of books in the school library, another 2,400 books were bought. At this time, the ratio of the number of books in the library to the original books is 1:3. How many books did the school originally have?
学校图书馆的图书借出总数的(11/15)后，又买来2400本，这时图书馆里的书和原来书的本数比是1：3，学校原来有图书多少本？
<gadget id="calculator">1 / 3</gadget>
<output>1/3 = around 0.333333</output>

<gadget id="calculator">11 / 15</gadget>
<output>11/15 = around 0.733333</output>

<gadget id="calculator">1 - (11/15)</gadget>
<output>4/15 = around 0.266667</output>

<gadget id="calculator">(1/3) - (4/15)</gadget>
<output>1/15 = around 0.066667</output>

<gadget id="calculator">2_400 / (1/15)</gadget>
<output>36_000</output>

<result>36_000</result>