I'll write log, you can use any base logs you like.
[tex](2/3)^x = 3.375=27/8[/tex]
[tex]x \log(2/3) = \log(27/8)[/tex]
[tex]x = \dfrac{\log(27/8)}{\log(2/3)}}[/tex]
[tex]x = \dfrac{\log( (3/2)^3)}{\log(2/3)}}[/tex]
[tex]x = \dfrac{\log( (2/3)^{-3})}{\log(2/3)}}[/tex]
[tex]x = \dfrac{-3 \log(2/3)}{\log(2/3)}}[/tex]
[tex]x = -3[/tex]
Answer: -3
