There are two bookshelves, A and B. It is known that there are 600 books in A bookshelf, borrow (1/3) from A bookshelf, and after borrowing 75% from B bookshelf, A bookshelf is twice as much as B bookshelf and 150 books more. How many books are there on the bookshelf?
甲、乙两个书架，已知甲书架有600本书，从甲书架借出(1/3)，从乙书架借出75%以后，甲书架是乙书架的2倍还多150本，乙书架原有多少本？
<gadget id="calculator">1 / 3</gadget>
<output>1/3 = around 0.333333</output>

<gadget id="calculator">1 - (1/3)</gadget>
<output>2/3 = around 0.666667</output>

<gadget id="calculator">600 * (2/3)</gadget>
<output>400</output>

<gadget id="calculator">400 - 150</gadget>
<output>250</output>

<gadget id="calculator">75 / 100</gadget>
<output>3/4 = around 0.75</output>

<gadget id="calculator">1 - (3/4)</gadget>
<output>1/4 = around 0.25</output>

<gadget id="calculator">250 / 2 / (1/4)</gadget>
<output>500</output>

<result>500</result>