Solve. Please provide in interval notation: x^3+9x^2-108>=0

factors to 
so we check the intervals
[-oo, -6]
(+)(-) so negative except at x=-6
[-6, 3]
(-)(+) so negative except at x=-6 and x=3

[3,oo]
(+)(+) positive

solution:
{-6} U [3, oo)