Answer
The electric force on the electron is in the +x direction.
Work Step by Step
We can find the strength of the electric field between $x = 1.0~cm$ and $x = 4.0~cm$:
$E = -\frac{\Delta V}{\Delta x}$
$E = -\frac{6.0~V-2.0~V}{0.040~m-0.010~m}$
$E = -133~V/m$
Since the electric field points from higher electric potential to lower electric potential, the electric field is in the -x direction.
Note that the charge on an electron is negative.
Since the electric force on a negative charge is in the opposite direction to the direction of the electric field, the electric force on the electron is in the +x direction.
