в) 3/4 a + 5/6 b - 1/8 a - 1/3 b;

Combine like terms: (3/4 a - 1/8 a) + (5/6 b - 1/3 b). Find common denominators: (6/8 a - 1/8 a) + (5/6 b - 2/6 b). Simplify: 5/8 a + 3/6 b = 5/8 a + 1/2 b.