Answer
The wave travels in the negative direction of the y axis.
Work Step by Step
We can write a general equation for the magnetic component:
$B = B_m~sin(ky+\omega~t)$
The term $ky$ shows that the wave travels along the y axis.
The term $+\omega t$ shows that the wave travels in the negative direction
The wave travels in the negative direction of the y axis.
