(7 целых -1 цел.5/12): 6,7+(5,75-3цел.1/6): 15,5 !

(7 - 1 5/12) / 6,7 + (5,75 - 3 1/6) / 15,5  = (5 7/12) / 67/10 + (5 3/4 - 3 1/6) / 15 1/2 = 67/12  / 67/10  + (5 9/12 - 3 2/12)  / 31/2 = 10/12 + (2 7/12)  / 31/2 = 5/6 + 31/12 /31/2 = 5/6 + 1/6 = 1