84. Решите уравнение: а) \(8-x=3\frac{7}{9}\); б) \(6\frac{1}{12}-b=2\frac{5}{12}\).

1. \[8-x=3\frac{7}{9},\qquad x=8-3\frac{7}{9}=4\frac{2}{9}.\]
2. \[6\frac{1}{12}-b=2\frac{5}{12},\qquad b=6\frac{1}{12}-2\frac{5}{12}=3\frac{8}{12}=3\frac{2}{3}.\]

Ответ: а) \(x=4\frac{2}{9}\); б) \(b=3\frac{2}{3}\).