\[9x - 5a = 2;\ \ \ \ \ \ x = 3;\ \ \ \ \ a - ?\]
\[3 \cdot 9 - 5a = 2\]
\[27 - 2 = 5a\]
\[25 = 5a\]
\[a = 5\]
\[Ответ:a = 5.\]