Answer
$4$
Work Step by Step
$\ln \left( 5+4x\right) -\ln \left( 3+x\right) =\ln 3\Rightarrow \ln \dfrac {5+4x}{3+x}=\ln 3$
$\Rightarrow \dfrac {5+4x}{3+x}=3\Rightarrow 5+4x=9+3x\Rightarrow x=4$
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