Q2) You can break the question into finding the sum of three different series (geometric series, arithmetic series, and a constant number) which all have n+2 terms (r=-1,0, 1, ...,n).

Q3) Please take note that you should the formulas for arithmetic and geometrical series as there is no information about the series. You should simply use a(n)=s(n)-s(n-1) to find the answer.