Electromagnetic Waves

An electromagnetic wave is propagating in vacuum along $-\hat{\mathbf{j}}$ direction. The magnetic field of the wave is given by $\mathbf{B}=\left(2 \times 10^{-8}\right) \cos \left[\pi \times 10^{15}\left(t+\frac{y}{c}\right)\right] \hat{\mathbf{k}} \mathrm{T}$. The electric field $\mathbf{E}$ of this wave is ( $c \equiv$ speed of light)