#### Answer

$\left\{ x| x=-\dfrac{10}{9}
\right\}
$

#### Work Step by Step

Using the properties of equality, the given equation, $
8x-(x+3)=-(2x+1)-12
,$ is equivalent to
\begin{array}{l}\require{cancel}
8x-x-3=-2x-1-12
\\\\
8x-x+2x=-1-12+3
\\\\
9x=-10
\\\\
x=-\dfrac{10}{9}
.\end{array}
Hence, the solution is $
\left\{ x| x=-\dfrac{10}{9}
\right\}
.$