ok
first, we see that they are not decreaseing by a common number (like 54 minus somethin=-18, then -18 minus something=6)
54/-18=-3
-18/6=-3
interesting
each is -3 times the previous
each term is divide the previous term by 3 and negative aka divide by -3
so nex term after 6 is 6/-3=-2
answer is -2