\[\boxed{\text{6.363.}}\]
\[\textbf{а)}\ 2,442\ :(6,8 - x) = 8,14\ \]
\[6,8 - x = 2,442\ :8,14\ \]
\[6,8 - x = 244,2\ :814\]
\[6,8 - x = 0,3\]
\[x = 6,8 - 0,3\]
\[x = 6,5.\ \]
\[Ответ:6,5.\ \]
\[\textbf{б)}\ 3,6 \cdot (1,3 + y) = 7,56\]
\[1,3 + y = 7,56\ :3,6\]
\[1,3 + y = 75,6\ :36\]
\[1,3 + y = 2,1\]
\[y = 2,1 - 1,3\]
\[y = 0,8.\ \]
\[Ответ:0,8.\ \]
\[\textbf{в)}\ 0,3n + 1,6n - 0,31 = 0,45\]
\[1,9n = 0,45 + 0,31\]
\[1,9n = 0,76\]
\[n = 0,76\ :1,9 = 7,6\ :19\]
\[n = 0,4.\ \]
\[Ответ:0,4.\ \]
\[\textbf{г)}\ 8,3m - 4m - 1,8m + 4,25 = 8\]
\[4,3m - 1,8m = 8 - 4,25\]
\[2,5m = 3,75\]
\[m = 3,75\ :2,5 = 37,5\ :25\]
\[m = 1,5\text{.\ }\]
\[Ответ:1,5.\]