Can anyone please help me with this?

The elevation of a hiking trail is modelled by the function h(x)=2x^3+3x^2−17x+12 where h is the height in meters above sea level and x is the horizontal distance from a ranger station in kilometers. If x<0, the position is to the west of the station, and if x>0 the position is to the east. Since the trail extends 4.2km to the west of the ranger station and 4km to the east, the model is accurate for {xεR|−4.2≤x≤4}. How can we determine which sections of the trail are above sea level?