Answer
9
Work Step by Step
Using the rules of logarithms to solve the equation, we find:
$$\log _6\left(3x\left(x-1\right)\right)=3 \\ 3x\left(x-1\right)=216 \\ x=9,\:x=-8$$
Checking for extraneous solutions, we see that only $x=9$ is valid.