Answer
$4+(9+x)=x+13$
Work Step by Step
Show that $4+(9+x)$ is equivalent to $x+13$.
$4+(9+x)\longrightarrow$ Use the associative property.
=$(4+9)+x\longrightarrow$ Use the commutative property.
=$x+(4+9)\longrightarrow$ Simplify.
=$x+13$