\[7,8x - 4,6x + 0,8 = 12\]
\[3,2x = 12 - 0,8\]
\[3,2x = 11,2\]
\[x = 11,2\ :3,2 = 112\ :32\]
\[x = 3,5\]
\[Ответ:x = 3,5.\]