\[a \cdot x = 7 + 3x\]
\[ax - 3x = 7\]
\[x(a - 3) = 7\]
\[x = \frac{7}{a - 3};\ \ a \neq 3.\]
\[a - 3\ должно\ быть\ делителем\ числа\ 7\]
\[(то\ есть\ равно \pm 1;\ \pm 7).\]
\[1)\ a - 3 = 1\]
\[при\ a = 4:\]
\[x = \frac{7}{1} = 7;\]
\[2)\ a - 3 = - 1\]
\[при\ a = 2:\]
\[x = \frac{7}{- 1} = - 7;\]
\[3)\ a - 3 = 7\]
\[при\ a = 10:\]
\[x = \frac{7}{7} = 1;\]
\[4)\ a - 3 = - 7\]
\[при\ a = - 4:\]
\[x = \frac{7}{- 7} = - 1.\]