7 / 8 - (1 / 3 - 1 / 12)
= 7 / 8 - 1 / 3 + 1 / 12
= 21 / 24 - 8 / 24 + 2 / 24
= 21 / 24 - 6 / 24
= 15 / 24
= 5 / 8