г) 3 4/21 - 5 1/12

1. Convert mixed numbers to improper fractions: 3 4/21 = 67/21, 5 1/12 = 61/12.
2. Rewrite the expression: 67/21 - 61/12.
3. Find a common denominator (84) and subtract: (268 - 427) / 84 = -159/84 = -53/28.