Erin is sorting through the library books to decide which ones to replace. She finds 8 less than 6 times as many obsolete books as damaged books. If she removes 69 books total, how many books were damaged? Let's think first. Chain of thought:
Let o be the number of obsolete books and d be the number of damaged books. We know that o + d = 69 and o = 6d - 8. Substituting the first equation into the second equation, we get 6d - 8 + d = 69. Combining like terms, we get 7d - 8 = 69. Adding 8 to both sides, we get 7d = 77. Dividing both sides by 7, we get d = 11.
Therefore, the answer is 11.