42 - (12 + 12/15 + 10 + 7/15)
= 42 - (22 + 7/15)
= 42 - 22 - 7/15
= 20 - 7/15
= 299/15
= 19 14/15

Therefore, 42 - (12 12/15 + 10 7/15) = 19 14/15