Answer
a. The –z direction.
b. The –z direction.
c. The +y direction.
d. The +y direction.
Work Step by Step
In each case, the direction of propagation is given by the direction of $\vec{E} \times \vec{B}$. The direction is perpendicular to the plane of $\vec{E}$ and of $\vec{B}$.
a. $\hat{i}\times(-\hat{j})=-\hat{k}$. The –z direction.
b. $\hat{j}\times \hat{i}=-\hat{k}$. The –z direction.
c. $-\hat{k}\times(-\hat{i})=\hat{j}$. The +y direction.
d. $\hat{i}\times(-\hat{k})=\hat{j}$. The +y direction.
