Answer:
the speed in -y
Explanation:
For this exercise we must use the right hand rule. The motion of a positive charge is given by.
Thumb points in the direction of speed
fingers extended in the direction of the magnetic field, + z axis
the palm in the direction of the force, as the charge is negative in the opposite direction of the force, axis + x
therefore the thumb is in the direction - y
the speed in -y