\[12x - (5x - 8) = 8 + 7x\]
\[12x - 5x + 8 = 8 + 7x\]
\[7x - 7x = 8 - 8\]
\[0x = 0\]
\[x - любое\ число.\]
\[Ответ:x - любое\ число.\]