ANSWER
[tex]\begin{equation*} 1.5*10^6\text{ N/C} \end{equation*}[/tex]EXPLANATION
The ratio of the electric field to the magnetic field for an electromagnetic wave is always equal to the speed of light.
This implies that:
[tex]\begin{gathered} \frac{E}{B}=c \\ \\ E=cB \end{gathered}[/tex]where c = speed of light = 300,000,000 m/s
Therefore, substitute the given values and solve for electric field amplitude, E:
[tex]\begin{gathered} E=300,000,000*5*10^{-3} \\ \\ E=1.5*10^6\text{ N/C} \end{gathered}[/tex]That is the answer.
