a)1/5+4/5.x=-3 b)|x|=6,8

#andy

\[\begin{array}{l}
a)\frac{1}{5} + \frac{4}{5}.x =  - 3\\
\frac{4}{5}x =  - 3 - \frac{1}{5}\\
\frac{4}{5}x =  - \frac{{16}}{5}\\
x =  - \frac{{16}}{5}:\frac{4}{5}\\
x =  - 4\\
b)\left| x \right| = 6,8\\
 \Leftrightarrow \left[ \begin{array}{l}
x = 6,8\\
x =  - 6,8
\end{array} \right.\\
 \Rightarrow S \in \{ 6,8; - 6,8\} 
\end{array}\]