Given, the electromagnetic wave is propagating in z i.e., +k^ direction.
The relation between the magnitudes of electric field, magnetic field and the speed of light is given by
∣B∣∣E∣=C
⇒∣E∣=∣B∣×C
⇒∣E∣=5×10−8×3×108=15Vm−1
We know that the direction of propagation of electromagnetic wave is along E×B.
So, E=15i^Vm−1