\[\boxed{\mathbf{111}.}\]
\[1)\ 25x - ax - 9 = 279\]
\[25x - ax = 279 + 9\]
\[x(25 - a) = 288\]
\[x = 16:\]
\[16 \cdot (25 - a) = 288\]
\[25 - a = 288\ :16\]
\[25 - a = 18\]
\[a = 25 - 18\]
\[a = 7.\]
\[Ответ:при\ a = 7.\]
\[2)\ (x + 14)\ :a = 13\]
\[x = 103:\]
\[(103 + 14)\ :a = 13\]
\[117\ :a = 13\]
\[a = 117\ :13\]
\[a = 9.\]
\[Ответ:при\ a = 9.\]