Answer
$x \approx 113.8$
Work Step by Step
First, add $6$ to both sides to get $$3\log(4x+9)=8$$ Next, divide both sides by $3$ to get $$\log(4x+9)=\frac{8}{3}$$ Since $10^a=10^b$ if $a=b$ and $10^{\log a}=a$, $$4x+9=10^{8/3}$$ Subtract $9$ from both sides to get $$4x=10^{8/3}-9$$ Divide both sides by $4$ to get $$x=\frac{10^{8/3}-9}{4}\approx113.8$$
