\[Пусть\ x\ страниц - в\ первой\ \]
\[рукописи;\]
\[y\ страниц - во\ второй\ рукописи.\]
\[Составим\ систему\ уравнений:\ \]
\[\left\{ \begin{matrix}
x - 60 = y\ \ \ \ \ \ \ \ \ \ \ \ \\
0,6x + 12 = 0,8y \\
\end{matrix} \right.\ \text{\ \ \ \ \ \ \ }\]
\[\left\{ \begin{matrix}
x - y = 60\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \\
0,6x - 0,8y = - 12\ \ \ | \cdot 5 \\
\end{matrix} \right.\ \text{\ \ \ \ \ }\]
\[\left\{ \begin{matrix}
x - y = 60\ \ \ | \cdot ( - 3) \\
3x - 4y = - 60\ \ \ \ \ \ \ \ \ \\
\end{matrix} \right.\ \]
\[\left\{ \begin{matrix}
- 3x + 3y = - 180\ \ \ (1) \\
3x - 4y = - 60\ \ \ \ \ \ \ \ \ \ (2) \\
\end{matrix} \right.\ \]
\[(1) + (2) \Longrightarrow - y = - 240\text{\ \ }\]
\[y = 240\]
\[\left\{ \begin{matrix}
y = 240\ \ \ \ \ \\
x - 60 = y \\
\end{matrix} \right.\ \text{\ \ \ \ \ \ }\]
\[\left\{ \begin{matrix}
y = 240\ \ \ \ \ \\
x = y + 60 \\
\end{matrix} \right.\ \text{\ \ \ \ \ }\]
\[\left\{ \begin{matrix}
y = 240\ \ \ \ \ \ \ \ \ \ \ \\
x = 240 + 60 \\
\end{matrix} \right.\ \text{\ \ \ \ \ }\]
\[\left\{ \begin{matrix}
y = 240 \\
x = 300 \\
\end{matrix} \right.\ \]
\[Ответ:\]
\[300\ страниц\ в\ первой\ рукописи;\]
\[240\ страниц\mathbf{\ во\ второй\ рукописи.}\]