What is the explicit rule for this geometric sequence? a1= 2/3; an = 9x an-1

Proceed as in example 3 in section 6.1 to rewrite the given expression using a single power series whose general term involves xk. ∞ n(n − 1)cnxn − 2 n = 2 − 4 ∞ ncnxn n = 1 + ∞ cnxn n = 0

I'm confused on this could anyone me and show me what i need to do to solve it.

Can someone me with this? i’m not sure what to put for my equations.