How to simplfy this indices question Grade 10 :$\frac{3^n-4 \cdot 3^{n-2}}{3^{n+1}-3^{n-1}}$ I am a student in grade 10 and i was given this question about indices 
$$\frac{3^n-4 \cdot 3^{n-2}}{3^{n+1}-3^{n-1}}$$
All I am capable to do is expanding it out, i.e. from $3^{n-2}$ to $3 \cdot 3^{-2}$. I am unable proceed to the next step, please show step by step solution! Thank you!

It is $$\frac{3^n-4\cdot 3^n\cdot \frac{1}{9}}{3^n(3-\frac{1}{3})}=\frac{3^n(1-\frac{4}{9})}{3^n(3-\frac{1}{3})}$$
