Opposites are the same difference from zero!
It would be the first one (x,-y) because say for example you take the point of v1 (4,-1) and reflect across x axis you get (4,1) for v
Since the deepest point of Death Valley is below sea level, its altitude is negative. So, the difference between the altitudes is

Subtracting a negative means to add, so we have

Answer:
The constant term is 6
The x³ term has a coeficient of 12
The resulting polynomial has degree 4