Notice that v points into the third quadrant since both of its components are negative. If you want a vector to point in the same direction, it would need to have the same sign on its components. So C is the correct choice.
The factor of 1/√80 comes from normalizing the vector v. Its norm/magnitude is
|v| = √((-4)² + (-8)²) = √(16 + 64) = √80
so the unit vector that points in the same direction as v is simply v / |v|.
