\[\frac{5x + 1}{6} - \frac{x + 3}{4} = 3\ \ \ \ \ \ \ | \cdot 12\]
\[2 \cdot (5x + 1) - 3 \cdot (x + 3) = 36\]
\[10x + 2 - 3x - 9 = 36\]
\[7x = 36 + 7\]
\[7x = 43\]
\[x = 6\frac{1}{7}.\]