Answer
$4C$
Work Step by Step
We are given that $log_{b}2=A$ and $log_{b}3=C$.
According to the power rule of logarithms, we know that $log_{b}M^{p}=plog_{b}M$ (when $b$ and $M$ are positive real numbers, $b\ne1$, and $p$ is any real number).
Therefore, $log_{b}81=log_{b}(3^{4})=4log_{b}3=4(C)=4C$.