2 7/9 * (3 3/4у - 11 2/3) + 1 6/7 = 2 4/21
2 7/9 * (3 3/4у - 11 2/3) = 2 4/21 - 1 6/7 = 2 4/21 - 1 18/21 = 7/21 = 1/3
3 3/4у - 11 2/3 = 1/3 : 2 7/9 = 1/3 : 25/9 = 1/3 * 9/25 = 3/25
3 3/4у = 3/25 + 11 2/3 = 9/75 + 11 50/75 = 11 59/75
у = 11 59/75 : 3 3/4 = 884/75 : 15/4 = 884/75 * 4/15 = 3536/1125
у = 3 целых 161/1125