[tex]\log(9)=\log_{10}(9)=\dfrac{\log_{5}(9)}{\log_{5}(10)}[/tex]
In my opinion, that is the simplest form. However, your teacher may want you to remove powers and factors of 5. In that case, the result is ...
[tex]=\dfrac{\log_{5}(3^{2})}{\log_{5}(5\cdot 2)}=\dfrac{2\log_{5}(3)}{1+\log_{5}(2)}[/tex]
