please help! urgent!!!

Given an arithmetic sequence in the table below, create the explicit formula and list any restrictions to the domain.


n an
1 9
2 3
3 −3
a) an = 9 − 3(n − 1) where n ≤ 9
b) an = 9 − 3(n − 1) where n ≥ 1
c) an = 9 − 6(n − 1) where n ≤ 9
d) an = 9 − 6(n − 1) where n ≥ 1