Question 21008
For the first series, divide the first number by 2 and add it to that number, and so on.  4 +4/2 = 6.   6 + 6/2 = 9.  9 + 9/2 = 13.5   13.5 + 13.5/2 = ?

for the next series,
divide each number by -3 as the next number.
12/(-3) = -4
-4/(-3) = 4/3
(4/3)/(-3) = -4/9
etc.