The books on the upper layer of a two-layer bookshelf are the lower layer (4/5). If 20 books are taken from the upper layer and placed in the lower layer, the ratio of the number of books on the upper and lower layers is 1:2. How many books are there in total on this bookshelf?
一个两层的书架上层放的书是下层的(4/5)，如果从上层取出20本放入下层，则上下两层放书数量的比是1：2．这个书架上一共放了多少本书？
<gadget id="calculator">4 + 5</gadget>
<output>9</output>

<gadget id="calculator">4 / 9</gadget>
<output>4/9 = around 0.444444</output>

<gadget id="calculator">1 + 2</gadget>
<output>3</output>

<gadget id="calculator">1 / 3</gadget>
<output>1/3 = around 0.333333</output>

<gadget id="calculator">(4/9) - (1/3)</gadget>
<output>1/9 = around 0.111111</output>

<gadget id="calculator">20 / (1/9)</gadget>
<output>180</output>

<result>180</result>