I am reviewing my teacher solution from test 2, and i cannot figure out what step he did to get to this last part. It is the inductive Step.

How do you get from here:

(3 * 3^(k+1) - 1) / 2

to this:

(3^(k+2) - 1) / 2 <---This is what comes next and is the final answer

Edit: Never Mind. I just figured it out after racking my brain on this.