\[y = kx + b;\ \ \ \ M\ (3;1);\ \ \ E\ (1;5).\]
\[\left\{ \begin{matrix} 3k + b = 1 \\ k + b = 5\ \ \\ \end{matrix} - \right.\ \text{\ \ \ \ \ \ \ \ \ \ \ \ \ }\]
\[\left\{ \begin{matrix} 2k = - 4\ \ \\ b = 5 - k \\ \end{matrix} \right.\ \text{\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ }\]
\[\left\{ \begin{matrix} k = - 2 \\ b = 7\ \ \ \\ \end{matrix} \right.\ \]
\[Уравнение\ прямой:\ \ \]
\[y = - 2x + 7.\ \]