Answer
$\{ \emptyset\}$ .
Work Step by Step
$log(11x+9)=3+log(x+3) \longrightarrow log(11x+9)=log10^3+log(x+3) \longrightarrow log(11x+9)=log(1000x+3000) \longrightarrow 11x+9=1000x+3000 \longrightarrow x=-\frac{2991}{989}$
Check the answer with the original equation, it does not fit. thus there is no solution or we have $\{ \emptyset\}$ .