80,5-(y-9 3/4)=28 5/6

80,5 - (у-9 3\4) = 28 5\6                                    80,5 = 80 5/10 = 80 1/2

80 1/2 - у + 9 3/4 = 28 5/6                              80 1/2 +9 3/4 =89 5/4 = 90 1/4

90 1/4 - у = 28 5/6

у = 90 1/4 - 28 5/6                           90 1/4 - 28 5/6 = 62 + (1/4 -5/6) = 62 -7/12 = 61 5/12

у = 61 5/12