6 целых 7/12 +(5 целых 3/40 - 4 целых 8/15)
6 7/12 + (5 3/40 - 4 8/15) = 79/12 + (203/40 - 64/15) = 79/12 + (3045/600 - 2560/600) = 79/12 + 485/600 = 79/12 + 97/120 = 790/120 - 97/120 = 693/120 = 231/40 = 5 31/40
Смотри решение во вложении