First:
\begin{equation}
\frac{\partial^2 E_z}{\partial x^2} = j \omega \mu_0 \frac{\partial H_y}{\partial x} = j^2 \omega^2 \mu_0 \epsilon_0E_z = -k_x^2E_z
\end{equation}
\begin{equation}
x = 3
\end{equation}
( x = 10 )
First:
\begin{equation}
\frac{\partial^2 E_z}{\partial x^2} = j \omega \mu_0 \frac{\partial H_y}{\partial x} = j^2 \omega^2 \mu_0 \epsilon_0E_z = -k_x^2E_z
\end{equation}
\begin{equation}
x = 3
\end{equation}
( x = 10 )