\[\left( 3x^{2} + 5x - 3 \right) - 3 \cdot \left( x^{2} + x + 4 \right) = 0\]
\[3x^{2} + 5x - 3 - 3x^{2} - 3x - 12 = 0\]
\[2x - 15 = 0\]
\[2x = 15\]
\[x = 15\ :2\]
\[x = 7,5.\]