A bookshelf has upper and lower layers, the ratio of the number of books on the upper and lower layers is 5:6, after taking 5 books from the upper layer and putting them into the lower layer, the ratio of the number of books on the upper and lower layers is 4:7. How many books were there on the shelf?
一个书架有上下两层，上下层数本数的比是5：6，从上层拿5本放入下层后，上下层数的比是4：7．书架上原来共有多少书？
<gadget id="calculator">5 + 6</gadget>
<output>11</output>

<gadget id="calculator">5 / 11</gadget>
<output>5/11 = around 0.454545</output>

<gadget id="calculator">4 / 11</gadget>
<output>4/11 = around 0.363636</output>

<gadget id="calculator">(5/11) - (4/11)</gadget>
<output>1/11 = around 0.090909</output>

<gadget id="calculator">5 / (1/11)</gadget>
<output>55</output>

<result>55</result>