 
 <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. <hau> Bari o ya zama adadin litattafan da suka tsufa kuma d ya zama adadin litattafan da suka lalace. Mun san cewa o + d = 69 da kuma o = 6d - 8. Sauya lissafi na farko a lissafi na biyu, muna samun 6d - 8 + d = 69. Idan muka hada abubuwa masu kama da juna, za mu samu 7d - 8 = 69. Ƙara 8 zuwa bangarorin biyu, muna samun 7d = 77. Idan muka raba bangarorin biyu da 7, za mu samu d = 11. Saboda haka, amsar ita ce 11. 