\[(3;\ - 2)\]
\[\left\{ \begin{matrix} 2x + ay = 8\ \ \\ bx + 3y = 15 \\ \end{matrix} \right.\ \text{\ \ \ \ \ \ \ }\]
\[\left\{ \begin{matrix} 6 - 2a = 8\ \ \\ 3b - 6 = 15 \\ \end{matrix} \right.\ \text{\ \ \ \ \ \ \ \ }\]
\[\left\{ \begin{matrix} 2a = - 2 \\ 3b = 21 \\ \end{matrix} \right.\ \text{\ \ \ \ \ \ \ \ }\]
\[\left\{ \begin{matrix} a = - 1 \\ b = 7\ \ \ \\ \end{matrix} \right.\ \]
\[Ответ:a = - 1;b = 7.\ \]