electromagnetic waves Questions

In a plane electromagnetic wave travelling in free space, the electric field component oscillates sinusoidally at a frequency of $2.0\times 10^{10}\text{Hz}$ and amplitude $48{\text{V m}}^{-1}$. Then the amplitude of the oscillating magnetic field is (Speed of light in free space $=3\times 10^8{\text{m s}}^{-1}$):