Answer
In region 4, the electric field points in the +x direction.
Work Step by Step
We can write the general equation for an electric field:
$E = -\frac{\Delta V}{\Delta x}$
We can see that the slope of the electric potential versus position graph is the negative of the electric field.
Note that the electric field always points from locations with higher electric potential to locations with lower electric potential.
In region 4, the slope of the electric potential versus position graph is negative.
Therefore, in region 4, the electric field points in the +x direction.
