What is the next term in the sequence below?

-321,108,-36,12, ...

This is a geometric sequence with a common ratio of - 1/3 and an initial term of - 324. Any geometric sequence can be expressed as:

a (n) = ar^ (n-1), in this case a=-324 and r=-1/3 so

a (n) = - 324 (-1/3) ^ (n-1) so the 5th term will be

a (5) = - 324 (-1/3) ^4

a (5) = - 324/81

a (5) = - 4