Answer
Option e.
The positive $z$-direction.
Work Step by Step
Using the right-hand rule for cross products, our thumb becomes the electric field vector, our pointer finger becomes the magnetic field vector, and our middle finger becomes the velocity vector.
The magnetic field is in the $-\hat j$ direction and the velocity is in the $+\hat i$ direction, and thus we need to point our middle finger to the left and our pointer finger downward.
If we stick out our thumb so that it is perpendicular to the plane that our middle and pointer finger makes ( (the $xy$-plane to be exact), then we see that our thumb is pointing in the $+\hat k$ direction, towards us, which is the positive $z$-direction.
Option e. is correct.
