Are 24 and 864 supposed to be negatives?
If so, that means that each term is multiplied by negative 6.
So, 4 times -6 = -24. Then -24 x -6 = 144. And so on.
So -864 x -6 = 5,184. (5th term)
5,184 x -6 = -31,104. (6th term)
-31,104 x -6 = 186,624. (7th term)
186,624 x -6 = -1,119,744. (8th term)
I think, and hope, that it is correct. Hope this helps! :)