Your answer to No. 1 is correct
2. arithmetic series with d = 4:_
an = 3 + 4(n-1)
3. this is a arithmetic sequence with a1 = 9 and d = -5
a128 = 9 -5(128-1) = -626
4. Geometric series with r = -2
an = a1 r^(n-1)
= -3* -2(n-1)
a97 = -3* -2^(97-1) = 4.75368975 * 10^29
