#### Answer

$x=-11$

#### Work Step by Step

$-3(x+1)-10=12+8$ $\longrightarrow$distributive property; simplify
$-3x-3-10=12+8$ $\longrightarrow$simplify
$-3x-13=20$ $\longrightarrow$addition property
$-3x-13+13=20+13$ $\longrightarrow$simplify
$-3x=33$ $\longrightarrow$multiplication property
$-3x\div-3=33\div-3$ $\longrightarrow$simplify
$x=-11$