velocity selector negatively, physics homework help

Please help me with the following question, answer and show the work you did to get to the solution, thank you i need help with this asap.
In a device called a velocity selector negatively charged particles are moving through a region of space with both an electric field and a magnetic field.  If the speed of the has a particular value, the net force acting on it is 0.  Assume that a negatively charged particle moves in the positive X-direction and that the electric field is in positive y-direction.  In which direction has the magnetic field to be in order to give a 0 net force?
Possible answers:
A- positive yB- positive zC- negative yD- negative z

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