Thanks for the fast reply. Okay, I know that you took out the 9 and put it on the outside and I know when you have something like but could you explain a little more how you got the new fraction in the second part where you have (subtracted exponents)?
For -11 I got infinity and 7 came out to negative infinity when put in the series. So both do not converge. But I still can't get the interval of convergence.