The magnitude of the electric field component of the electromagnetic wave is given by

$E_0=200 \mathrm{V} {\mathrm{m}}^{-1}$

The formula to calculate the intensity of the electromagnetic wave is given by

$I=\frac{1}{2}{\epsilon }_{\mathit{0}}c{E}_{\mathit{0}}^{\mathit{2}} ...\left(1\right)$

From equation (1), it follows that

$\begin{array}{rcl}I& =& \frac{1}{2}\times 8.85\times {10}^{-12}\times 3\times {10}^8\times {\left(200\right)}^2 \mathrm{W} {\mathrm{m}}^{-2}\\ & =& 53.1 \mathrm{W} {\mathrm{m}}^{-2}\end{array}$