 <translate> 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. <yor> Jẹ́ kí o jẹ́ iye ìwé tí kò wúlò mọ́ àti d jẹ́ iye ìwé tí ó bàjẹ́. A mọ̀ pé o + d = 69 àti o = 6d - 8. Tí a bá fi àfikún àkọ́kọ́ sí àfikún kejì, a ó rí 6d - 8 + d = 69. Tá a bá pa àwọn ọ̀rọ̀ tó jọra pọ̀, a máa rí 7d - 8 = 69. Tá a bá fi 8 kún ìhà méjèèjì, a máa rí 7d = 77. Tá a bá pín ìhà méjèèjì sí méje, a máa rí i pé d=11. Nítorí náà, ìdáhùn rẹ̀ jẹ́ mọ́kànlá. 