\[12 - 4 \cdot (x - 3) = 39 - 9x\]
\[12 - 4x + 12 = 39 - 9x\]
\[- 4x + 9x = 39 - 24\]
\[5x = 15\]
\[x = 3.\]
\[Ответ:x = 3.\]