3 1/7+2 7/8 3 1/7-2 7/8
3 1/7 + 2 7/8 = 3 8/56 + 2 49/56 = 5 57/56 = 6 целых 1/56 3 1/7 - 2 7/8 = 3 8/56 - 2 49/56 = 2 64/56 - 2 49/56 = 15/56