Recursion problem T(n)=3T(n/3)+3n

Question

I just need help solving this problem. I know I'm supposed to be using the Master's Theorem but I don't know where to start

Answer 1

$$T(n)=3T\left(\frac n3\right)+3n=9T\left(\frac n9\right)+3\frac n3+3n=27T\left(\frac n{27}\right)+3\frac n{27}+3\frac n3+3n=\cdots$$

So for an exact power of $3$, you get

$$nT(1)+3\frac{3n-3}2.$$