#### Answer

$x=3$

#### Work Step by Step

Using the properties of equality and combining like terms, the value of the variable that satisfies the given equation, $
3x+9+4x=30
,$ is
\begin{array}{l}\require{cancel}
3x+4x=30-9
\\\\
7x=21
\\\\
x=\dfrac{21}{7}
\\\\
x=3
.\end{array}