Answer
$1 Nm^{2}/C$
Work Step by Step
Electric flux $\phi$ through any surface is given as:
$ \phi= E.A=EAcos\theta$
Here,
$\theta=\frac{\pi}{2}-30^{\circ}=\frac{\pi}{3}$
$E=200 N/C$, $A= 10\times 10cm^{2}=10^{-2}m^{2}$
Hence,
$\phi=200 \times10^{-2}\times\frac{\pi}{3}$$=2\times\frac{1}{2}=1 Nm^{2}/C$
