Answer:
The magnitude is
The direction is the positive x axis
Explanation:
From the question we are told that
The electric field is E = 450 V/m in the negative y ‑direction
The speed of the proton is in the positive z direction
Generally the overall force acting on the proton is mathematical represented as
Now for the beam of protons to continue un-deflected along its straight-line trajectory then
So
=>
Generally from unit vector cross product vector multiplication
So the direction of B (magnetic field must be in the positive x -axis )
So
=>
=>
=>
=>
=>