Решение уравнений:

1. a) $$\frac{1}{3}x = 12$$ $$ x = 12 \cdot 3 = 36$$ $$\boxed{x = 36}$$
2. в) $$5x - 4,5 = 3x + 2,5$$ $$ 5x - 3x = 2,5 + 4,5$$ $$ 2x = 7$$ $$ x = \frac{7}{2} = 3,5$$ $$\boxed{x = 3,5}$$
3. б) $$6x - 10,2 = 0$$ $$ 6x = 10,2$$ $$ x = \frac{10,2}{6} = 1,7$$ $$\boxed{x = 1,7}$$
4. г) $$2x - (6x - 5) = 45$$ $$ 2x - 6x + 5 = 45$$ $$ -4x = 40$$ $$ x = -10$$ $$\boxed{x = -10}$$