(42 5/7 - 4 2/5) - (23 - 15 9/14) = 30 67/70
1) 42 5/7 - 4 2/5 = 42 25/35 - 4 14/35 = 38 11/35
2) 23 - 15 9/14 = 22 14/14 - 15 9/14 = 7 5/14
3) 38 11/35 - 7 5/14 = 38 22/70 - 7 25/70 = 37 92/70 - 7 25/70 = 30 67/70
ответ: 30 целых 67/70.
