\[x\ рублей - открытка;\ \ \]
\[y\ рублей - конверт.\]
\[\left\{ \begin{matrix} 5x + 4y = 44\ \ \ | \cdot 2 \\ 2x + 3y = 26\ \ \ | \cdot 5 \\ \end{matrix} \right.\ \text{\ \ \ \ \ \ \ }\]
\[\left\{ \begin{matrix} 10x + 8y = 88\ \ \ \ \ \\ 10x + 15y = 130 \\ \end{matrix} \right.\ \text{\ \ }( - )\]
\[\overline{\ \ \ \ \ \ - 7y = - 42\ \ \ \ \ \ }\text{\ \ }\]
\[\ \ \ \ \ \ \ \ \ \ \ y = 6\]
\[\left\{ \begin{matrix} y = 6\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \\ 2x + 3 \cdot 6 = 26 \\ \end{matrix} \right.\ \text{\ \ \ \ \ \ \ }\]
\[\left\{ \begin{matrix} y = 6\ \ \ \\ 2x = 8 \\ \end{matrix} \right.\ \text{\ \ \ \ \ \ \ }\]
\[\left\{ \begin{matrix} y = 6 \\ x = 4 \\ \end{matrix} \right.\ \]
\[Ответ:\ \ 4\ рубля;\ 6\ рублей.\ \ \]