A basic log transition is #x=log_b(a)# to #a=b^x#.
If you plug in the variables of #a=1/9#, #b=3#, and #x=-2#, you can go from #a=b^x# (or #3^-2=1/9# if you input the variables) to #x=log_b(a)#, which is equivalent to #-2=log_3(1/9)# if you plug in the variables.