6log3(x−3)=−24

Do you mean 

$$\\6log_3(x-3)=-24\\\\ log_3(x-3)=-4\\\\ 3^{log_3(x-3)}=3^{-4}\\\\ x-3=3^{-4}\\\\ x-3=\frac{3^{-4}}{1}\\\\ x-3=\frac{1}{3^{+4}}\\\\ x-3=\frac{1}{81}\\\\ x=3\frac{1}{81}\\\\$$