#### Answer

$30-x=3(x+6)$
$x=3$

#### Work Step by Step

$30-x=3(x+6)$ $\longrightarrow$distributive property
$30-x=3x+18$ $\longrightarrow$addition property
$30-x-18+x=3x+18-18+x$ $\longrightarrow$simplify
$12=4x$ $\longrightarrow$multiplication property
$12\div4=4x\div4$ $\longrightarrow$simplify
$3=x$