The new numbers after subtracting remainders are:

285-9 = 276

1249-7 = 1242

Prime factors of 276 = 23 × 3 × 2

Prime factors of 1242 = 2 × 3 × 3 × 3 × 23

Therefore HCF of 276 and 1242 is: 2 × 3 × 23 = 138

Hence the greatest number which divides 285 and 1249 leaving remainder 9 and 7 respectively is138