Elly is organizing her books on the new bookcases her parents bought her. Each of the middle 2 shelves can hold 10 books. The bottom shelf can hold twice as many books as a middle shelf. The top shelf can hold 5 fewer books than the bottom shelf. If she has 110 books, how many bookcases does she need to hold all of them?
The bottom shelf can hold 2 * 10 = 
<gadget id="calculator">2*10</gadget>
<output>20</output>
20 books.
The 2 middle shelves can hold a total of 2 * 10 = 
<gadget id="calculator">2*10</gadget>
<output>20</output>
20 books.
The top shelf can hold 20 - 5 = 
<gadget id="calculator">20-5</gadget>
<output>15</output>
15 books.
Each bookcase can hold a total of 20 books + 20 books + 15 books = 
<gadget id="calculator">20+20+15</gadget>
<output>55</output>
55 books.
To hold all of her books, she needs 110 / 55 = 
<gadget id="calculator">110/55</gadget>
<output>2</output>
2 bookcases.

<result>2</result>