\[ \frac{3x + 20}{6} + \frac{x}{3} = \frac{3x + 20}{6} + \frac{2x}{6} = \frac{3x + 20 + 2x}{6} = \frac{5x + 20}{6} \]
\[ \frac{1 - 2x}{4} = \frac{5x + 20}{6} \]
\[ 12 \cdot \frac{1 - 2x}{4} = 12 \cdot \frac{5x + 20}{6} \]
\[ 3(1 - 2x) = 2(5x + 20) \]
\[ 3 - 6x = 10x + 40 \]
\[ 3 - 40 = 10x + 6x \]
\[ -37 = 16x \]
\[ x = \frac{-37}{16} \]
Ответ: \( x = -\frac{37}{16} \).