Ответ:
\[\left\{ \begin{matrix} a + b + c = 10 \\ a = 2b\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \\ a - 5 = c\ \ \ \ \ \ \ \ \ \ \\ \end{matrix} \right.\ .\]
\[\left\{ \begin{matrix} a + b + c = 10 \\ a = 2b\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \\ a - 5 = c\ \ \ \ \ \ \ \ \ \ \\ \end{matrix} \right.\ .\]