\[(a - 2)x = 9 + 3a\]
\[(a - 2) \cdot 5 = 9 + 3a\]
\[5a - 10 = 9 + 3a\]
\[2a = 19\]
\[a = 9,5\]
\[Ответ:при\ a = 9,5.\]