3. б) 4-2a 6a-12

б) $$ \frac{4 - 2a}{6a - 12} = \frac{-2(-2 + a)}{6(a - 2)} = \frac{-2(a - 2)}{6(a - 2)} = -\frac{2}{6} = -\frac{1}{3} $$

Ответ: $$ -\frac{1}{3} $$